Experimental density measurements of bis(2-ethylhexyl) phthalate at elevated temperatures and pressures

J. Chem. Thermodynamics 63 (2013) 102–107

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Experimental density measurements of bis(2-ethylhexyl) phthalate at elevated temperatures and pressures Babatunde A. Bamgbade a,b,⇑, Yue Wu a,b, Hseen O. Baled a,c, Robert M. Enick a,c, Ward A. Burgess a, Deepak Tapriyal a,d, Mark A. McHugh a,b a

National Energy Technology Laboratory, Office of Research and Development, Department of Energy, Pittsburgh, PA 15236, USA Chemical and Life Science Engineering Department, Virginia Commonwealth University, Richmond, VA 23284, USA Chemical and Petroleum Engineering Department, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15261, USA d URS, Pittsburgh, PA, USA b c

a r t i c l e

i n f o

Article history: Received 21 December 2012 Received in revised form 4 April 2013 Accepted 6 April 2013 Available online 12 April 2013 Keywords: Phthalate High pressure Density Peng–Robinson PC-SAFT

a b s t r a c t Experimental high-temperature, high-pressure (HTHP) density data for bis(2-ethylhexyl) phthalate (DEHP) are reported in this study. DEHP is a popular choice as a reference fluid for viscosity calibrations in the HTHP region. However, reliable HTHP density values are needed for accurate viscosity calculations for certain viscometers (e.g. rolling ball). HTHP densities are determined at T = (373, 424, 476, 492, and 524) K and P to 270 MPa using a variable-volume, high-pressure view cell. The experimental density data are satisfactorily correlated by the modified Tait equation with a mean absolute percent deviation (d) of 0.15. The experimental data are modeled with the Peng–Robinson (PREoS), volume-translated PREoS (VTPREoS), and perturbed chain statistical associating fluid theory (PC-SAFT EoS) models. The required parameters for the two PREoS and the PC-SAFT EoS models are determined using group contribution methods. The PC-SAFT EoS performs the best of the three models with a d of 2.12. The PC-SAFT EoS is also fit to the experimental data to obtain a new set of pure component parameters that yield a d of 0.20 for these HTHP conditions. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction Bis(2-ethylhexyl) phthalate (DEHP) has been suggested as a reference fluid for viscosity measurements in the high-temperature, high-pressure (HTHP) region [1–3]. Prior to that, diisodecyl phthalate (DIDP) has been used as a reference fluid for moderately high viscosities in the range of (50 to 125) mPa  s [2–11]. However, DIDP is commercially available only as a mixture of several phthalates esters of the isomers of isodecyl alcohols which limits the application of DIDP as a reference fluid [2,3]. Conversely, DEHP, obtained from the reaction of phthalic anhydride with 2-ethylhexanol, has the advantage of being available as a pure compound and, hence, DEHP is a better choice as the reference fluid for calibration of viscometers over wide pressure ranges [1,3]. Experimental density and viscosity data are reported for DEHP at pressures in excess of 1000 MPa in an ASME report in the 1950s [12]. In the report, experimental viscosities are reported at temperatures to 492 K, however, the density data are only reported to temperatures of 372 K. Therefore, HTHP density data for DEHP at temperatures to 525 K and pressures to 270 MPa are presented here. ⇑ Corresponding author. Address: Chemical and Life Science Engineering Department, Virginia Commonwealth University, 601 West Main St., Richmond, VA 23284, USA. Tel.: +1 571 315 2199. E-mail address: [email protected] (B.A. Bamgbade). 0021-9614/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jct.2013.04.010

In the present work, a variable-volume, high-pressure view cell is used for the determination of the single phase pure component density of DEHP at temperatures and pressures to 525 K and 270 MPa, respectively. The density data, obtained at six different temperatures, are correlated with the modified Tait equation [13] which contains three fitted parameters. Moreover, the HTHP density data obtained in this study are used to test the performance of both cubic and SAFT-based equations of state. The Peng–Robinson cubic equation of state (PREoS) [14] and the volume-translated, PREoS (VT-PREoS) [15] are used to model the experimental data. The Perturbed Chain Statistical Associating Fluid Theory equation of state (PC-SAFT EoS) [16], with first order group contribution parameters by Tihic et al. [17] is also used to model the experimental data. Moreover, a new set of HTHP PC-SAFT parameters is obtained from the fit of the PCSAFT EoS to the experimental HTHP density data obtained in this study.

2. Experimental 2.1. Material DEHP, shown here, was purchased from Sigma Aldrich (purity mass fraction = 0.99). The DEHP was used as received.

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103

experimental uncertainty, Uc, is Uc(q) = 0.70%  q (at k = 2 for an interval having a confidence level of approximately 95%) where q is a density data point. 3. Results and discussion

FIGURE 1. Chemical structure of DEHP.

Table 1 lists the experimental DEHP densities as functions of temperature and pressure obtained in this study. Figure 3 shows the effect of pressure, to 270 MPa, on the density of DEHP at different temperatures. The density of DEHP ranges from (811 to 1046) kg  m3 in the temperature and pressure ranges investigated. 3.1. Modified Tait equation fit to the data

2.2. Experimental method Figure 2 shows a schematic diagram of the high-pressure view cell used in this study. The detailed description of the apparatus has been given elsewhere [18–20] and is only briefly described here. The desired operating pressure of the cell is obtained by displacing an internal piston with water pressurized using a highpressure generator. The system pressure is measured on the water-side of the piston using a pressure transducer (Viatran Corporation, Model 245, 0 to 345 MPa) with an uncertainty of 0.07 MPa to pressures of (56 and 0.35) MPa for pressures from (56 to 275) MPa. The temperature of the cell contents is measured by a type-k thermocouple (Omega Corporation), calibrated at four different temperatures, against a precision immersion thermometer (Fisher Scientific, 308 to 473 K, precise to 0.1 K, accurate to better than 0.1 K, recalibrated by ThermoFisher Scientific Company at four different temperatures using methods traceable to NIST standards). The experimentally-observed temperature variation for each reported isotherm is within 0.2 K. The internal volume of the cell is determined using a linear, variable, differential transformer (LVDT, Schaevitz Corp., Model 2000 HR) that tracks the location of the internal floating piston as shown in figure 2B. The piston position is correlated to the internal view cell volume by calibrations done at (323, 423, and 523) K using n-decane whose density is reported by NIST to a maximum value of 770 kg  m3 or to maximum operating conditions of 800 MPa and 673 K [21]. The expanded uncertainty in volume calibration is estimated to be within 0.65% of the calculated volume. Prior to loading, the cell is flushed with CO2 three times to remove residual air that does not dissolve in the DEHP whereas residual CO2 readily dissolves in DEHP. Typically, between 7.0 and 8.5 g of DEHP are loaded into the cell for an experiment. The cell is heated to a desired temperature and pressurized to a select pressure and the piston position is recorded to obtain a data point. For any given isotherm, data are obtained at random pressures to minimize any experimental artifacts in the measurements. The standard uncertainties, u, are u(T) = 0.20 K, u(P) = 0.07 MPa below (56 and 0.35) MPa from (56 to 275) MPa, and the estimated accumulated (combined)

Equation (1) shows the modified Tait equation where Po equals 0.1 MPa, qo is the density at Po and B and C are parameters determined from a fit of the Tait equation to experimental density data as explained in detail elsewhere [20].

q  qo PþB ¼ Clog10 : Po þ B q

ð1Þ

The Tait equation is fit to each isotherm independently to obtain initial values for qo, B, and C by minimizing the mean absolute percent deviation (d) as defined in equation (2). The parameters qo and B are then fit to quadratic functions of temperature as shown in equations (3) and (4) while the parameter C is treated as a constant that is averaged over all isotherms. Finally, the averaged value of C, along with the original coefficients of equations (3) and (4) are simultaneously refit to all of the 132 data points by minimizing d.

d¼

   n  1X qi;experimental  qi;Tait    100;  n 1  qi;experimental 

B=MPa ¼

2 X bi ðT=KÞi ;

ð2Þ

ð3Þ

i¼0

qo =ðkg  m3 Þ ¼

2 X

ai ðT=KÞi :

ð4Þ

i¼0

Table 2 lists a summary of the Tait equation parameters for each isotherm investigated in this study, while figure 3 shows that the Tait equation provides a very good representation of DEHP densities. Parameter C has a value of 0.2275, which is comparable to the values found for several hydrocarbon systems [19,22–24]. Parameters for equations (3) and (4) are listed in table 3. The Tait equation, with the parameters listed in table 3, are used to compare density data obtained in this study with the data of Agaev et al. [25], reported with an uncertainty of 0.03%, from (373.29 to 523.15) K to a maximum pressure of 80 MPa. The d from

FIGURE 2. Schematic diagram of (A) the high-pressure view cell used in this study, and (B) the linear variable differential transformer (LVDT) used for volume measurements.

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TABLE 1 Experimental density data, q, at different temperatures, T, and pressures, P, for DEHP obtained in this study.a T/K 373.29 ± 0.1

FIGURE 3. Comparison of DEHP density data, q, (symbols) obtained at different pressures, P, in this study to a fit of the modified Tait equation (lines). Temperatures are 373.3 K (D), 423.4 K (d), 476.2 K (s), 491.9 K (h), 523.7 K (j).

this comparison is less than 0.60, which is less than the estimated accumulated experimental uncertainty in the data reported in the present study. In fact, a d value of 0.57 is obtained when comparing data of Agaev et al. to those predicted with the Tait equation from T = (303.15 to 548.15) K, which are temperatures well outside the range used to determine the Tait parameters in the present study. Hence, it is reasonable to conclude that the Tait equation provides a reliable method to estimate DEHP densities from (303.15 to 548.15) K and pressures to 270 MPa.

423.53 ± 0.1

476.20 ± 0.1

P/MPa

q/kg  m3

P/MPa

q/kg  m3

P/MPa

q/kg  m3

3.8 7.6 12.2 15.9 18.1 22.3 28.3 34.8 42.2 48.9 56.1 69.5 83.7 104.2 125.4 138.9 152.9 174.4 208.3 240.0 262.1

921 924 928 931 933 936 940 945 950 954 959 967 974 984 994 1001 1007 1015 1029 1041 1046

4.2 7.9 11.1 14.5 18.0 21.2 27.8 35.2 42.1 49.2 55.7 70.7 83.7 104.2 125.4 139.9 153.7 173.4 207.1 239.4 263.8

878 885 890 895 898 901 908 914 918 924 930 939 948 960 970 977 983 992 1006 1018 1028

5.5 9.5 9.4 15.7 15.2 15.2 27.5 27.3 26.8 46.9 46.7 59.8 71.5 70.7 96.4 95.7 114.8 114.2 140.4 139.8 176.2 206.9 240.2 269.0

847 853 853 861 861 861 874 874 874 894 894 905 913 914 931 931 942 942 958 959 975 990 1002 1013

T/K

3.2. Density predictions

491.86 ± 0.1

The DEHP density data obtained in this study are modeled with the Peng–Robinson equation of state, (PREoS) [14], a volume-translated modification of the PREoS, (VT-PREoS) [15], and the Perturbed Chain Statistical Associating Fluid Theory equation of state (PC-SAFT EoS) [16]. The performance of each model is characterized by the d as shown in equation (5).

   n  1X qi;experimental  qi;calculated  d¼   100:    n 1 qi;experimental

ð5Þ

3.2.1. Peng–Robinson and volume-translated Peng–Robinson equations Nikitin et al. report Tc(±10 K) and Pc(±0.04 MPa) for DEHP obtained using a pulse-heating method [26] since phthalates undergo thermal decomposition at temperatures below their critical temperatures [26,27]. These critical properties are used with the PREoS and VT-PREoS models to calculate DEHP density and these results are compared to calculations using these models with three different group contribution methods to estimate the critical properties [28–30]. The acentric factor, x, is calculated according to equation (6) [30], where Tb is the boiling temperature (K) and Pc is the critical pressure in atmospheres.

2 T  3 b 3 4 Tc x ¼  T 5log10 ðPc =atmÞ  1: 7 1 b

ð6Þ

Tc

It is not surprising that the PREoS poorly represents the results with d values as high as 30, given that each of the sources yield very high values of x, beyond values recommended for use with the PREoS [14,32]. Baled et al. [15] improved the performance of the PREoS to model hydrocarbon densities in the HTHP region by introducing a volume correction parameter, c. Baled et al. correlated c as a linear function of reduced temperature, Tr = T/Tc, with

523.6 ± 0.1

P/MPa

q/kg  m3

P/MPa

q/kg  m3

3.9 4.1 3.9 10.5 9.9 23.3 23.3 22.8 37.5 37.2 51.1 50.7 71.5 71.9 95.0 94.8 121.7 121.8 145.4 145.6 177.2 177.4 204.3 206.0 230.8 229.4 253.7 258.1

830 830 831 839 840 856 856 856 870 870 885 886 902 902 918 918 934 934 948 948 964 964 977 978 988 989 998 1000

5.7 9.2 9.2 16.1 16.1 21.6 21.6 27.5 27.3 35.7 35.5 44.4 44.6 44.3 44.2 56.3 55.8 68.9 68.5 82.5 82.2 97.3 97.0 117.0 117.7 117.4 155.7 156.1 181.5 181.2 209.5 209.9 233.9 234.0 253.6 253.4 263.5

811 817 817 827 827 835 835 842 842 851 851 860 860 860 860 871 871 882 882 892 893 903 903 916 916 916 939 939 952 952 964 964 974 974 983 983 987

a Standard uncertainties, u, are u(T) = 0.20 K, u(P) = 0.07 MPa below (56 and 0.35) MPa from (56 to 270) MPa and the estimated accumulated (combined) experimental uncertainty, Uc, is Uc(q) = 0.70%  q (k = 2).

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chains rather than hard spheres. The chain and association terms in the original SAFT equation remain unchanged in the PC-SAFT equation. However, the dispersion term is modified. The reduced residual Helmholtz free energy for non-associating fluids, such as DEHP, is given as

TABLE 2 Tait equation parameters, qo, B, and C, the mean absolute percent deviation, d, and the standard deviation, k, values obtained for each density isotherm, T. C has a constant value of 0.2275. T/K

qo/kg  m3

B/MPa

d

k

373.3 423.5 476.2 491.9 523.7

918 878 839 823 799

103.621 76.074 55.210 50.590 43.438

0.09 0.18 0.11 0.16 0.23

0.06 0.13 0.09 0.07 0.11

e a res ¼ e a hc þ e a disp ; e hc

ð8Þ

e disp

where a and a are the reduced hard chain reference and dispersion terms, respectively. For a single-component fluid,

ahc ¼ mahs  ðm  1Þ lnðg hs Þ; TABLE 3 Parameters, ai and bi, used in equations (3) and (4) to predict qo(T) and B(T) obtained from the fit of the Tait equation to the high-pressure density isotherms reported in this study and with C equal to 0.2275. ao  103

a1  101

a2  104

bo  105

b1  103

b2

1.1812

6.4578

1.6000

5.4233

1.7277

1.4800

ahs ¼

g hs ¼

coefficients A and B correlated to the acentric factor and molecular weight of the compound of interest [15], where V represents the molar volume and the subscript experimental represents experimental data.

c ¼ V PREoS  V experimental ¼ A þ B  T r :

4g  3g2 ð1  gÞ2

ð9Þ

;

ð10Þ

;

ð11Þ

2g 2ð1  gÞ3

adisp ¼ 2pqm2



e



kB T

r3 I1 ðg; mÞ  pqCm3



e

2

kB T

r3 I2 ðg; mÞ: ð12Þ

hs

Here, a represents the reduced Helmholtz free energy of the hardsphere fluid, g hs is the hard-sphere radial distribution function, m is the number of segments in a molecule, kB is Boltzmann’s constant, and g is the reduced fluid density also known as the segment packing fraction. I1 and I2 are calculated from power series in density as given in [16]. The parameters q, r, and e/kB, are the total number density, temperature-independent segment diameter, and the interaction energy, respectively. Parameter C is given as

ð7Þ

Table 4 lists the critical properties and acentric factor from four different sources used in this study along with the d and k calculated from the fit of the data using the VT-PREoS model. The d values for the VT-PREoS model are less than 10 except when using the parameters reported by Constantinou and Gani [29], in which case it is higher than 20. The reason for this high d value is not apparent when using the VT-PREoS along with the group contribution approach of Constantinou and Gani [29] to model DEHP density data. However, consider the performance of the VT-PREoS model when the DEHP critical properties are adjusted slightly. The d with the VT-PREoS for the 373 K isotherm can be reduced to 7.7 rather than 23.4 if the Constantinou and Gani value of Tc is used along with a Pc of 1.220 MPa, rather than the Constantinou and Gani value of 0.982 MPa, and with a newly calculated x of 0.551, rather than 0.415. Given that the adjusted critical properties and acentric factor are within the range of the values reported in table 4, it is reasonable to conclude that a volume translated cubic-based equation of state is not capable of accurately modeling the density of such a high molecular weight, polar compound.

C¼

1þm

8g  2g2 ð1  gÞ4

þ ð1  mÞ

20g  27g2 þ 12g3  2g4

!1

½ð1  gÞð2  gÞ2

: ð13Þ

The density at a given temperature and pressure is determined by adjusting the value of the reduced density, g, to minimize the difference between the calculated pressure and the system pressure. Therefore, the density is calculated knowing the system temperature, pressure, and the three, pure-component parameters, m, r, and e/kB. In this study, the HTHP density data of DEHP are modeled with the PC-SAFT EoS using two different approaches to obtain the pure component parameters. In the first approach, the first order group contribution method (GC PC-SAFT) proposed by Tihic et al. [17] is used to calculate DEHP pure component parameters. As shown in figure 1, DEHP has an aromatic core and two, long-chain, ester arms. The DEHP core contains four aromatic carbons, each with a single hydrogen atom, whose group contribution value is listed as an ACH group by Tihic and coworkers. Each of the other two carbons in the aromatic ring (denoted as AC) contains one ester group (denoted as COO) connected to a long chain saturated, branched alkyl group containing one methine (denoted as ACH<), five methylene (denoted as ACH2), and two methyl groups (denoted as ACH3). Each GC PC-SAFT parameter is calculated as a sum of the contributions from the

3.2.2. PC-SAFT EoS SAFT-based equations of state are constructed from a summation of the reduced, residual Helmholtz free energies that account for hard sphere formation, dispersion interactions, and chain formation resulting from segments bonding to one another, as well as intra- and inter-molecular hydrogen bonding and other specific interactions. For the original SAFT equation [33], the Helmholtz free energy of dispersion is calculated for a reference fluid of hard spheres. However, for the case of the PC-SAFT EoS [16], the Helmholtz free energy term is calculated for a reference fluid of hard

TABLE 4 Critical temperature, Tc, critical pressure, Pc, and acentric factor, x, from four different sources, along with the mean absolute percent deviation (d) and the standard deviation (k) obtained using the volume-translated Peng–Robinson (VT-PREoS). The normal boiling point of DEHP, Tb, is 657.2 K and the molecular weight is 390.56 g/ml [31].

Nikitin et al. [26] Marrero and Gani [28] Constantinou and Gani [29] Reid et al. [30]

Tc/K

Tb/Tc

Pc/MPa

x

d PREoS

k PREoS

d VT-PREoS

k VT-PREoS

835.0 868.7 853.5 806.8

0.787 0.757 0.770 0.815

1.070 1.220 0.982 0.989

0.622 0.439 0.415 0.863

21.29 14.03 29.32 24.50

2.54 2.72 2.25 2.50

7.65 2.22 21.72 9.74

2.11 1.71 1.99 2.02

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TABLE 5 Performance of the two PC-SAFT EoS approaches considered in this study. GC PC-SAFT utilizes pure component parameters, m, r, and e/kB, determined from the first order group contribution method of Tihic et al. [17]. HTHP PC-SAFT utilizes pure component parameters determined from a simultaneous fit of all of the density isotherms reported in this study. The mean absolute percent deviation, MAPD and standard deviation, SD, for both approaches are also listed. EoS model

m

r

e/kB

d

k

GC PC-SAFT HTHP PC-SAFT

10.873 15.497

3.750 3.321

274.351 249.031

2.12 0.20

0.63 0.19

this instance, there are more than one set of parameters that give satisfactory density predictions since only the fit of liquid density data is used as the criteria for determining the parameters [34]. When fitting liquid density data, changing the value of e/kB has less of an effect on the fit than changing the values for m and r. For example, the d decreases from (2.12 to 1.32) when e/ kB is changed from (275 to 250) while using m and r from the GC method. However, the d increases by more than an order of magnitude if either m and/or r are changed from the GC values to those from the fit of the PC-SAFT EoS to the data, while using the e/kB from the GC method. 4. Conclusion

FIGURE 4. Deviation plot for the HTHP PC-SAFT EoS fit to experimental DEHP density data obtained in this study. 373.3 K (D), 423.4 K (d), 476.2 K (s), 491.9 K (h), 523.7 K (j).

groups. Second order group contribution parameters are not considered because the parameters accounting for the exact arrangements of groups present in DEHP, such as the ortho positioning of the two ester groups on the aromatic ring, have not been published. It is worth noting that Tihic et al. [17] reported first order group contribution parameters for an aromatic carbon connected to a methine group (ACCH<), a methylene group (ACCH2A), and to a methyl group (ACCH3). However, Tihic and coworkers do not report first order group contribution parameters for an aromatic carbon connected to an ester group (ACCOO). The GC PC-SAFT EoS overpredicts the HTHP density data for DEHP at all of the temperatures and pressures considered in this study. The d for these calculations is 2.12 as listed in table 5 and the overprediction is as much as 3% at the high end of the HTHP pressure range. Nevertheless, these results demonstrate the utility of using a first order group contribution method with the PC-SAFT equation of state as compared to a cubic equation of state when calculating the density of a high molecular weight compound. It is worth noting that the trends in the calculated densities using the PC-SAFT equation with GC parameters are similar to the modeling trends for HTHP densities of saturated alkanes from pentane to eicosane [18,19] when using parameters fit to low pressure density and vapor pressure data. In the second approach, the PC-SAFT EoS is fit simultaneously to all of the HTHP density isotherms reported in this study to obtain pure component parameters for DEHP. Table 5 shows that the performance of the PC-SAFT EoS is greatly improved in this instance with better d values. Figure 4 also shows the good fit of calculations with the HTHP PC-SAFT EoS to the experimental data. For these calculations the pure component parameters estimated from the first order group contribution approach are used as initial guesses and new set of parameters, m, r, and e/kB, are calculated by minimizing the d of the calculated and experimental densities. Note that the set of parameters obtained with the second approach differ from the set obtained with the GC method. In

In this study, the high-temperature, high-pressure experimental density data for DEHP at temperatures from (373 to 525) K and pressures to 270 MPa are reported with a maximum experimental uncertainty of 0.70%. The density data are correlated to the modified Tait equation that provides a means for interpolating the density over a range of temperatures from (373 to 525) K and pressures to 270 MPa. PREoS-based and SAFT-based EoS are employed to model the DEHP density data. The calculated densities determined with the PREoS-based equations are very sensitive to the values of Tc, Pc, and x that are determined from experiment or calculated from group contribution methods. The results suggest that a cubicbased equation of state cannot be used to reliably calculate the density of such a high molecular weight compound at high temperatures and pressures. In contrast, here it is shown that reliable densities can be calculated with the PC-SAFT EoS combined with first order group contribution methods of Tihic et al. [17]. The trends observed with the GC PC-SAFT EoS are similar to those observed with the PC-SAFT modeling of hydrocarbons from pentane to eicosane. Unfortunately, the complete set of second order group contribution parameters for DEHP are not available for comparison to the results obtained with the first order parameters. Acknowledgments This technical effort was performed in support of the National Energy Technology Laboratory’s Office of Research and Development support of the strategic Center for Natural Gas and Oil under RES contract DE-FE0004000. References [1] L. Lugo, J.J. Segovia, M. Carmen Martin, J. Fernandez, M.A. Villamanan, J. Chem. Thermodyn. 49 (2012) 75–80. [2] K.R. Harris, S. Bair, J. Chem. Eng. Data 52 (2007) 272–278. [3] K.R. Harris, J. Chem. Eng. Data 54 (2009) 2729–2738. [4] X. Paredes, O. Fandino, M.J.P. Comunas, A.S. Pensado, J. Fernandez, J. Chem. Thermodyn. 41 (2009) 1007–1015. [5] X. Paredes, O. Fandino, A.S. Pensado, M.J.P. Comunas, J. Fernandez, J. Chem. Thermodyn. 44 (2012) 38–43. [6] F.J.P. Caetano, J. Fareleira, C. Oliveira, W.A. Wakeham, Int. J. Thermophys. 25 (2004) 1311–1322. [7] F.J.P. Caetano, J. Fareleira, C. Oliveira, W.A. Wakeham, J. Chem. Eng. Data 50 (2005) 1875–1878. [8] F.J.P. Caetano, J.M.N.A. Fareleira, A.C. Fernandes, C.M.B.P. Oliveira, A.P. Serro, I.M. Simoes de Almeida, W.A. Wakeham, Fluid Phase Equilib. 245 (2006) 1–5. [9] F.J.P. Caetano, J.M.N.A. Fareleira, A.P. Froeba, K.R. Harris, A. Leipertz, C.M.B.P. Oliveira, J.P.M. Trusler, W.A. Wakeham, J. Chem. Eng. Data 53 (2008) 2003– 2011. [10] F. Peleties, J.J. Segovia, J.P.M. Trusler, D. Vega-Maza, J. Chem. Thermodyn. 42 (2010) 631–639. [11] A.P. Froeba, A. Leipertz, J. Chem. Eng. Data 52 (2007) 1803–1810. [12] R.V. Kleinschmidt, D. Bradbury, M. Mark, Viscosity and density of over forty lubricating fluids of known composition at pressures to 150,000 psi and temperatures to 425 F, ASME, New York, 1953. [13] J.H. Dymond, R. Malhotra, Int. J. Thermophys. 9 (1988) 941–951. [14] D. Peng, D.B. Robinson, Ind. Eng. Chem. Fundam. 15 (1976) 59–64.

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JCT 12-738