J. of Supercritical Fluids 115 (2016) 65–78 Contents lists available at ScienceDirect The Journal of Supercritical Fluids journal homepage: www.elsevier.com/locate/supflu Implementation of GC-PPC-SAFT and CP-PC-SAFT for predicting thermodynamic properties of mixtures of weakly- and non-associated oxygenated compounds Helena Lubarsky a , Ilya Polishuk a,∗ , Dong NguyenHuynh b,∗ a b Department of Chemical Engineering & Biotechnology, Ariel University, 40700, Ariel, Israel Petrovietnam Manpower Training College, No.43 30/4(A1) Street, Ward 9, Vung Tau City, Vietnam a r t i c l e i n f o Article history: Received 29 February 2016 Received in revised form 23 April 2016 Accepted 23 April 2016 Available online 30 April 2016 Keywords: Predictive modeling SAFT Thermodynamic properties Global phase behavior a b s t r a c t This study continues a comprehensive comparison between the Critical Point-based Modified PC-SAFT (CP-PC-SAFT) and the Group Contribution Polar PC-SAFT (GC-PPC-SAFT). The predictive values of these approaches are enhanced by reducing their referring to the experimental pure compound data. The mixtures comprising aromatic and aliphatic alkanols, esters, ethers and ketones have been treated in the entirely predictive manner, without adjusting any binary parameters. The results indicate that both models under consideration are particularly accurate estimators of single phase liquid densities at high pressures, usually with slight superiority of GC-PPC-SAFT. Nevertheless the universality of CP-PC-SAFT could be considered as more advanced since this model yields accurate predictions also for sound velocities and compressibilities. In addition, the results indicate that GC-PPC-SAFT is often a superior estimator of phase equilibria in symmetric systems. At the same time, CP-PC-SAFT typically has a clear advantage in predicting the global phase behavior of asymmetric systems. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Simultaneous estimation of various kinds of fluid phase equilibria and the single phase thermodynamic properties in wide range of operating conditions is one of the major industrial requirements posed to modern thermodynamic approaches [1]. The literature dealing with modeling of phase equilibria by Equation of State (EoS) approaches is virtually immense and it has been surveyed by several comprehensive reviews and monographs [2–7]. In the recent years accurate estimation of the auxiliary thermodynamic properties by the EoS models receives major attention as well. In this respect several versions of the Statistical Association Fluid Theory (SAFT) present particular interest. Among the recent studies, the applications of SAFT-VR [8–12], Soft-SAFT [13–17], SAFT + cubic [18–25], PC-SAFT [26,27], modified PC-SAFT [28,29], and other versions of SAFT [30–33] for estimating the derivative thermodynamic properties should be noticed. Unfortunately, wide industrial implementation of most SAFT approaches is hindered by lacking of ∗ Corresponding authors. E-mail addresses: polishuk@ariel.ac.il (I. Polishuk), dongnh@pvmtc.com.vn (D. NguyenHuynh). http://dx.doi.org/10.1016/j.supflu.2016.04.013 0896-8446/© 2016 Elsevier B.V. All rights reserved. standardization in evaluating their substance-specific parameters [1], while fitting of large experimental databases diminishes their predictive values. This problem can be addressed by a standardized numerical solution of the substance-dependent parameters at the characteristic states, namely the pure compound critical and triple points, as proposed by the critical point-based modified version of PC-SAFT (CP-PC-SAFT). Thus far it has been demonstrated that CP-PC-SAFT yields accurate predictions of various thermodynamic properties of substances such as light compounds, n-alkanes, 1-alkenes [34], 1-alkanols [35], aromatic and haloaromatic compounds [36], some haloalkanes [37,38], and their mixtures in wide range of conditions. In addition, it has been found that this model can be applied in predictive manner for estimating solubility of metallic mercury in hydrocarbons [39]. A conceptually different method for enhancing the predictive character of SAFT models is evaluation of their substance-specific parameters by the group contribution approaches. One of these approaches is the Group Contribution Polar PC-SAFT (GC-PPC-SAFT). Thus far GC-PPC-SAFT has been successfully implemented for modeling various phase equilibria in mixtures of polycyclic aromatic hydrocarbons [40], heavy esters [41], CO2 -n-alkanes, methane-n-alkanes, and ethane-n-alkanes [42], CO2 , N2 , and H2 S-aromatic hydrocarbons and n-alkanes, [43], H2 -hydrocarbon mixtures [44], methyl 66 Table 1 Accuracy of predicting thermophysical data in mixtures in the single-phase region (k12 = 0). Property AAD% CP-PC-SAFT AAD% GC-PC-SAFT T range (K) P range (bar) No. pts. Refs. ethylene(1) – 1-pentanol(2) ethylene(1) – 1-heptanol(2) ethylene(1) – 1-nonanol(2) ethylene(1) – vinyl acetate(2) cyclohexane(1) – 1-butanol(2) 1-hexene(1) – 1-butanol(2) n-hexane(1) – 1-hexanol(2) n-hexane (1) – 1-hexanol(2) n-heptane(1) – 1-heptanol(2) n-heptane(1) – 1-heptanol(2) n-heptane(1) – 1-heptanol(2) n-heptane(1) – 2-methyl-2-butanol(2) n-heptane(1) – 2-methyl-2-butanol(2) n-heptane (1) – 1-decanol(2) isooctane(1) – 1-butanol(2) n-nonane(1) – 1-octanol(2) n-nonane(1) – 1-octanol(2) n-nonane(1) –1-octanol(2) dimethyl carbonate(1) – n-hexane(2) dimethyl carbonate(1) – n-octane(2) dimethyl carbonate(1) – n-decane(2) dimethyl carbonate(1) – p-xylene(2) diethyl carbonate(1) – n-octane(2) diethyl carbonate(1) – n-C10 H22 (2) diethyl carbonate(1) – p-xylene(2) dibutyl ether(1) – 1-butanol(2) dibutyl ether(1) – 1-butanol(2) dibutyl ether(1) – 1-butanol(2) dibutyl ether(1) – 1-hexanol(2) dibutyl ether(1) – 1-hexanol(2) dibutyl ether(1) – 1-hexanol(2) methyl benzoate(1) – 1-hexanol(2) methyl benzoate(1) – 1-hexanol(2) methyl benzoate(1) – 1-hexanol(2) density density density density density density density isobaric thermal expansivity density isothermal compressibility isobaric thermal expansivity density sound velocity sound velocity density sound velocity density adiabatic compressibility density density density density density density density density isothermal compressibility isobaric thermal expansivity density isothermal compressibility isobaric thermal expansivity density isothermal compressibility isobaric thermal expansivity 3.37 4.17 3.49 3.595 1.180 1.58 0.650 11.0 0.913 3.53 5.28 1.25 1.26 1.90 1.83 1.23 0.670 3.13 1.38 1.36 0.968 0.419 0.993 0.951 0.284 0.896 3.23 6.32 0.952 5.74 4.41 0.433 5.91 5.14 1.53 2.09 2.02 – 0.956 1.17 1.11 6.08 0.785 20.5 5.20 – – 9.92 – 9.56 0.639 20.8 – – – – – – – 2.34 16.1 3.18 2.20 22.9 6.00 2.05 25.9 7.12 298–373 298–373 298–413 298–373 293–333 273–333 303–423 303–503 298–393 298–393 298–393 293–318 292–318 293–319 273–333 293–423 303–453 333–453 293–313 278–353 288–308 288–308 288–308 288–308 288–308 293–393 293–393 293–393 293–353 293–353 293–353 278–358 278–358 278–358 500–1950 500–1950 500–1950 500–1950 1–1000 1–500 0.9–506 69–3476 1–1400 1–1400 1–1400 1–1000 1–1013 1–1013 1–500 0.98–1013 0–980 0–980 1–400 1–400 1–400 1–400 1–400 1–400 1–400 1–1400 1–1400 1–1400 1–1400 1–1400 1–1400 1–600 1–600 1–600 75 75 99 75 495 200 160 660 680 680 680 696 450 401 360 325 185 171 360 905 144 180 180 162 216 445 445 445 300 300 300 1134 1134 1134 [54] [54] [54] [54] [55] [56] [57] [58] [59] [59] [59] [60] [60] [61] [62] [63,64] [65] [65] [66] [67,68] [68] [69] [68] [68] [69] [70] [70] [70] [71] [71] [71] [72] [72] [72] H. Lubarsky et al. / J. of Supercritical Fluids 115 (2016) 65–78 System H. Lubarsky et al. / J. of Supercritical Fluids 115 (2016) 65–78 67 6 2400 (b) (a) P(bar) P(bar) 1600 4 800 2 0 0 100 T (K) 180 260 0.0 340 150 .2 .4 x1,y1 .6 .8 1.0 150 P(bar) 100 (d) P(bar) 318.15 K 100 298.15 K (c) 50 50 K 343.8 K 313.3 282.9 K 0 0 0.0 .2 .4 x1,y1 .6 .8 1.0 0.0 .2 .4 x1,y1 .6 .8 1.0 Fig. 1. Phase equilibria in the systems of nitrogen(1), methane(1), krypton(1) and xenon(1) – dimethyl ether (DME)(2). (a) the near-critical isopleths: 䊎 – N2 (1) – DME(2) – CH4 (1) – DME(2) (x1 = 0.38), – Kr(1) – DME(2) (x1 = 0.69). The isotherms: (b) Xe(1) – DME(2) at 182.33 K, (c) CH4 (1) – DME(2), (d) N2 (1) – DME(2). Points (x1 = 0.6), – experimental data [73–75,96–98]. Dashed lines – predictions of CP-PC-SAFT, solid lines – of GC-PPC-SAFT (k12 = 0 for both models and all the current and the furtherly considered systems). benzoate-alkanes [45], methanol-n-alkanes [46], water-alkanes, aromatic hydrocarbons, alcohols and gases [47], ethers, aldehydes and ketones [48], CO2 -1, 2, 3 and 4-alkanols [49], and additional polar compounds [50–52]. In the previous study [53] we have compared the performances of CP-PC-SAFT and GC-PPC-SAFT in estimating various thermodynamic properties of the pure weakly- and non-associated alkanols, ethers, esters and ketones in wide range of temperatures and pressures. It has been demonstrated that both models are capable of predicting reasonable accurate results for various thermodynamic properties in the particularly wide range of conditions. It has also been found that CP-PC-SAFT typically has an advantage in predicting sound velocity and compressibility data. At the same time GC-PPC-SAFT is superior in qualitative estimating the isobaric thermal expansion coefficients and the vapor pressures away from the critical points. The current investigation aims at comparing the predictions of CP-PC-SAFT and GC-PPC-SAFT for the mixtures of the previously considered [53] compounds, and it continues paying a major attention to the high pressure range. Unlike the relative paucity of the pertinent data on the single phase thermodynamic properties [54–72], vast number of references report phase equilibria in various mixtures of the compounds under consideration. Some of these references [73–78] provide information concerning the global phase behavior in several systems of these substances. Obviously, such data are essential for the fundamental comparison between the models and, consequently, they are considered as a primary subject of the current investigation. At the same time, it should be emphasized that a very accurate modeling of even the most sophisticated phase equilibria can be achieved by fitting the binary adjustable parameters. Although the predictive values of EoS models can be recovered by further generalization of these parameters, this practice may hinder a comparison between the EoS models. Therefore, similarly to the recent studies of Bender et al. [79,80], here the values of all binary adjustable parameters are also set to zero in all the considered cases. The subsequent discussion provides some additional information on the current implementation of CP-PC-SAFT and GCPPC-SAFT. 2. Theory Both approaches under considerations have been described in great details in the previous references [34–52]. Hence the current discussion is restricted to the mean features of these models and the major differences between them. The predictive character of CP-PC-SAFT is enhanced by a substantial reduce of the data required for evaluating its substancespecific parameters. Instead of fitting these parameters to large and vague experimental databases, they are solved at two characteristic states, namely the critical and the triple points, by implementing a standardized numerical procedure. Unfortunately, the original version of PC-SAFT [81] cannot generate the simultaneously accurate description of the critical temperature and pressures along with the sub-critical data [82]. In addition, this model is affected by 68 H. Lubarsky et al. / J. of Supercritical Fluids 115 (2016) 65–78 (a) (b) Fig. 2. Phase equilibria in: (a) nitrogen(1) – 1-decanol(2), (b) methane(1) – 1-butanol(2). Points – experimental data [99,100]. Dashed lines – predictions of CP-PC-SAFT, solid lines – of GC-PPC-SAFT. 10 8 UCEP EP LC n 240 6 P(bar) 4 270 160 290 310 330 80 0 270 380 T(K) Fig. 3. Critical loci and endpoints of ethane(1) – 1-alkanols(2) systems: 䊎 – 1-butanol, data [76,77]. Dashed lines – predictions of CP-PC-SAFT, solid lines – of GC-PPC-SAFT. certain undesired numerical artefacts [83–91]. In order to address these issues and to improve the over-all accuracy of CP-PC-SAFT, the original version of PC-SAFT [81] has been substantially revised [34]. In particular, its universal parameters of the radial distribution function in 1st order perturbation term have been transformed, the expressions of the hard sphere contribution and the tempera- 490 – 1-pentanol, 600 – 1-octanol. Experimental endpoints – LCEP 䊉 – UCEP. Experimental ture dependence of the segment diameter have been changed, and the mixing rules have been slightly modified. Besides the advantages of CP-PC-SAFT in estimating thermodynamic properties in particularly wide range of conditions for large variety of compounds [34–39], there is a price to pay for implementation of its standardized predictive procedure. In particular, this model may H. Lubarsky et al. / J. of Supercritical Fluids 115 (2016) 65–78 (a) 69 (b) (d) (c) Fig. 4. LLVE in: (a,b) ethane(1) – 1-octanol(2), (c,d) xenon(1) – 1-decanol(2) systems. Points – experimental data [77,78]. Dashed lines – predictions of CP-PC-SAFT, solid lines – of GC-PPC-SAFT. generate imprecise estimations of the vapor pressures away from the critical points. In addition, an accuracy of the CP-approach deteriorates in the cases of heavy compounds whose critical data are imaginary, and the strongly associated substances. Unfortunately, attaching this model by an association contribution does not result in substantial improvement of its accuracy. Therefore the current version of CP-PC-SAFT [34–39] neglects these interactions, while the strongly associated compounds are excluded from its applicability range. Unlike CP-PC-SAFT, GC-PPC-SAFT does not revise the original version of PC-SAFT [81], but comprises two additional contributions, namely the association and the multi-polar terms. The latter contribution has been obtained by extending the theory of Gubbins and Twu [92] to chain molecules using the “segment approach” of Jog and Chapman [93] and Jog et al. [94]. The current GC method has been originally proposed by Tamouza et al. [95] and furtherly expanded to various chemical groups [40–52]. The latter references also list the experimental data selected for developing this approach. Currently it is implemented for evaluating ε (the segment energy parameter), (the segment diameter), and m (the number of segments), while other model’s parameters are kept constant for the homologies series of compounds in order to maintain its predictive character. Notwithstanding of its advantageous accuracy and significant predictive capacity, GC-PPC-SAFT has two major drawbacks. In particular, being based on the original form of PC-SAFT [81], this model overestimates the pure compound critical temperature and pressures. In addition, the current GC method does evolve most 2nd order functional groups, which typically affects its predictions for the branched molecules. Moreover, the GC method cannot be implemented for the first members of the homologues series of compounds. In all these cases the molecular parameters of the model are not predicted, but fitted to the available experimental data. Unfortunately, some particularly important data reporting the global phase behavior are available specifically for the systems of compounds, such as dimethyl ether and benzyl alcohol, which cannot be appropriately treated by the current version of GC-PPC-SAFT in predictive manner. Although in the latter cases the comparison with CP-PC-SAFT can hardly be recognized as entirely equivalent, such systems have still been included in this study. The GC-PPCSAFT parameters for the gases have been adopted from the original version of PC-SAFT [81]. The values of the molecular parameters, either solved by CP-PC-SAFT, predictively assembled and the fitted for GC-PPC-SAFT are listed in the Supplementary Content (Tables S1 and S2). All the calculations have been performed in Mathematica® 7 software and the pertinent routines can be obtained from the corresponding authors by request. 3. Results In order to compare the performances of the models under consideration in comprehensive manner, we have implemented them for predicting various data thus far reported for the mixtures of oxygenated compounds. First of all, the available single phase thermodynamic properties in wide range of conditions have been considered. Afterwards the models under consideration have been implemented for predicting the existing information on the global phase behavior, the representative high pressure VLE in systems of gases such as nitrogen, methane, ethane, carbon dioxide, etc. 70 H. Lubarsky et al. / J. of Supercritical Fluids 115 (2016) 65–78 180 180 P(bar) (a) P(bar) 120 120 60 60 (b) 323.1 K 323 .1 K 313.15 K 5K 313.1 0 0 0.0 .2 .4 x1,y1 .6 .8 1.0 0 ρ (g/L) 300 600 900 210 200 P(bar) (c) P(bar) (d) 150 140 K 15 8. 4 4 K 3.3 35 100 5 K 328 .1 338 50 5 318.1 .15 70 K 309 K K 0 0 0.0 .2 .4 x1,y1 .6 .8 1.0 0.0 .2 .4 x1,y1 .6 .8 1.0 Fig. 5. VLE in ethane(1) – 1-alkanols(2) systems: (a and b) 1-butanol, (c) 1-octanol, (d) 1-decanol. Points – experimental data [100–104]. Dashed lines – predictions of CP-PC-SAFT, solid lines – of GC-PPC-SAFT. and the oxygenated organic compounds (furtherly designated as asymmetric), systems of compounds existing in the liquid phase at the ambient conditions or having comparable critical constants (furtherly designated as symmetric), and, finally, the characteristic low pressure phase equilibria data. Table 1 compares the absolute average deviations (AAD%) yielded for the single phase densities, isobaric thermal expansivities, isothermal and adiabatic compressibilities, and sound velocities covering the high pressure range. Unfortunately, the current version of GC-PPC-SAFT cannot be applied in predictive manner for the particularly important systems of vinyl acetate, 2-methyl-2-butanol, dimethyl carbonate and diethyl carbonate. In these cases we report only the results of CP-PC-SAFT. As seen, both models yield satisfactorily accurate predictions for the densities. Remarkable, in most of the cases GC-PPC-SAFT has a slight superiority in estimating these data. At the same time, the precision of CP-PC-SAFT in predicting the densities of n-hexane(1) – 1hexanol(2), dimethyl and diethyl carbonates(1) – p-xylene(2) and methyl benzoate(1) – 1-hexanol(2) should be noticed. In addition, both models typically exhibit the comparable over-all results for the isobaric thermal expansivities. However in the cases of sound velocities and compressibilities the picture is different. Yet CPPC-SAFT has a major advantage, confirming the previously drown conclusion [53] concerning its universality in the elevated pressure range. In the following discussion let us proceed to consideration of phase equilibria. Fig. 1 depicts phase equilibria in the systems of dimethyl ether with nitrogen, methane, krypton and xenon, including the global phase behavior represented by the near-critical isopleths. Wallbruch et al. [73] have related the extent of phase separation in these systems to the polarizability of the pertinent gases. In particular, it has been explained that the smaller polarizability of nitrogen resulting in the relatively large excess functions in its mixtures with the polar dimethyl ether, and, consequently, wide region of phase separation (phase behavior of Type III). At the same time, the bigger polarizabilities of the other gases reduce the extent of phase separation, resulting in phase behavior of Type II for methane and krypton systems, and, apparently, Type I in the case of xenon. In spite of the fact that CP-PC-SAFT does not consider the polar interactions, it correctly predicts the topology of the global phase behavior for all these systems. Unfortunately, this is not a case of GC-PPCSAFT. Although its predictions are similar to CP-PC-SAFT for the nitrogen system (Fig. 1A and D), GC-PPC-SAFT erroneously predicts the Type III topology for other systems as well, substantially overestimating the extent of their phase separation (Fig. 1A–C). At the same time, although the over-all quantitative predictions of CP-PCSAFT can be considered as satisfactorily accurate, it exhibits a minor underestimation of the phase split in methane (Fig. 1A) and xenon (Fig. 1B) systems. As seen, the latter tendencies are valid also in the cases of 1alkanols. In particular, both models continue yielding alike results for nitrogen(1) – 1-decanol (Fig. 2A) with certain superiority of CP-PC-SAFT. In the case of methane(1) – 1-butanol (Fig. 2B) GCPPC-SAFT once again overestimates the phase equilibria. Although CP-PC-SAFT predicts these data more accurately, apparently it slightly underestimates them. Similar results are obtained also for ethane(1) – 1-alkanols(2). As seen (Fig. 3), GC-PPC-SAFT continues predicting the Type III for these systems, substantially overes- H. Lubarsky et al. / J. of Supercritical Fluids 115 (2016) 65–78 71 330 300 P(bar) (a) P(bar) (b) 220 200 100 3 37 .15 K 110 .1 5 338 K .15 343 K 1 318. 5K 0 0 0.0 .2 .4 x1,y1 .6 .8 0.0 1.0 .2 .4 x1,y1 .6 .8 1.0 100 (c) P(bar) (d) 44 8.1 5 P(bar) K 330 75 220 8.1 40 5K 50 110 25 15 K 318. 5K 308.1 0 0 0.0 .2 .4 x1,y1 .6 .8 1.0 0.0 .2 .4 x1,y1 .6 .8 1.0 Fig. 6. VLE in: (a) ethylene(1) – 1-pentanol(2), (b) ethylene(1) – 1-octanol(2), (c) ethylene(1) – 1-decanol(2) and (d) propane – 1-decanol(2) systems. Points – experimental data [103–106]. Dashed lines – predictions of CP-PC-SAFT, solid lines – of GC-PPC-SAFT. timating an extent of the phase split at the low temperature range. Although CP-PC-SAFT correctly estimates their Type IV phase behavior, its tendency of minor underestimating of the phase equilibria takes place also in this case. Fig. 4A–B provide additional details concerning the three-phase equilibria in the representative system ethane(1) – 1-octanol(2) and Fig. 4C–D – in xenon(1) – 1-decanol(2). As seen, similarly to the previously considered system xenon(1) – dimethyl ether(2), GC-PPC-SAFT substantially over-estimates the phase split. Although CP-PC-SAFT truthfully estimates the equilibria compositions of the liquid phases and the loop created by the densities, its quantitative predictions the latter property are less accurate. Fig. 5 depicts the predictions of VLE in ethane(1) – 1-alkanols(2). As seen, although CP-PC-SAFT exhibits the superior over-all quality of predictions, GC-PPC-SAFT estimates slightly more accurately the phase equilibria at the moderated pressures. In addition, it can be seen (Fig. 5D), that at the high temperature (448.15 K) both models yield nearly identical results, overestimating the solubility of ethane in the liquid 1-decanol rich phase. Fig. 6A–C demonstrate that a tendency detected for the previously considered systems of light alkanes and polar compounds, namely the overestimation of phase equilibria by GC-PPC-SAFT and the superior over-all accuracy of CP-PC-SAFT, are valid also in the case of ethylene(1) – 1-alkanol(2) systems. Once again, the performances of both models under consideration become hardly distinguishable at the elevated temperatures (Fig. 6D). However, unlike the previously considered ethane(1) – 1-decanol(2), in the case of propane(1) their predictions are particularly accurate. In addition to the discussed above mixtures of 1-alkanols, comprehensive experimental data are available also for their carbon dioxide systems. Unfortunately, accurate modeling of these systems requires fitting of two binary adjustable parameters of CP-PC-SAFT [36] and implementation of a sophisticated crossassociation interaction scheme for GC-PPT-SAFT [49]. Since this study examines only the entirely predictive capacities of these models without adjusting any binary parameters, we treat here CO2 as a non-associative and non-polar molecule, and, therefore, omit the carbon dioxide(1)–alkanol(2) systems. In the following discussion the results for the systems of additional oxygenated compounds are presented. Fig. 7 depicts the high pressure phase diagrams of the systems of two aromatic compounds, namely methyl benzoate and benzyl alcohol with ethane and carbon dioxide. As indicated previously, the molecular parameters of GC-PPC-SAFT for these aromatic compounds have not been assembled by the GC method, but fitted to the experimental data. The figure shows that this time the tendencies exhibited by the approaches under consideration become quite opposite. In particular, unlike the previously considered cases, yet CP-PC-SAFT predicts a larger extent of phase equilibria in comparison to GC-PPC-SAFT. As seen, in the cases of ethane(1) – benzyl alcohol(2) (Fig. 7A), carbon dioxide(1) – benzyl alcohol(2) (Fig. 7C) and carbon dioxide(1) – methyl benzoate(2) (Fig. 7D) this tendency of CP-PC-SAFT is in a better over-all agreement with the experimental data. Fig. S1 in the Supplementary Content demonstrates that CP-PC-SAFT truthfully predicts the phase equilibria in ethane and carbon dioxide systems of additional aromatic compounds. Nevertheless, Fig. 7B 72 H. Lubarsky et al. / J. of Supercritical Fluids 115 (2016) 65–78 330 300 P(bar) (a) P(bar) (b) 220 200 100 3 37 .15 K 110 .1 5 338 K .15 343 K 1 318. 5K 0 0 0.0 .2 .4 x1,y1 .6 .8 0.0 1.0 .2 .4 x1,y1 .6 .8 1.0 100 (c) P(bar) (d) 44 8.1 5 P(bar) K 330 75 220 8.1 40 5K 50 110 15 318. 25 K 5K 308.1 0 0 0.0 .2 .4 x1,y1 .6 .8 1.0 0.0 .2 .4 x1,y1 .6 .8 1.0 Fig. 7. VLE in: (a) ethane(1) – benzyl alcohol(2), (b) ethane(1) – methyl benzoate(2), (c) carbon dioxide(1) – benzyl alcohol(2) and (d) carbon dioxide(1) – methyl benzoate(2) systems. Points – experimental data [107–111]. Dashed lines – predictions of CP-PC-SAFT, solid lines – of GC-PPC-SAFT. indicates that this tendency of CP-PC-SAFT to predict a wider area of VLE is not always in better agreement with the data. Although this model is slightly more accurate in estimating the solubility of ethane in methyl benzoate at the moderated pressures, GC-PPCSAFT yields the advantageous over-all results for this system. In addition, GC-PPC-SAFT is apparently a better estimator of the vapor phase compositions. Unlike the relative scarcity of the high pressure phase equilibria of oxygenated aromatic compounds, a more significant experimental data base is available for the systems of carbon dioxide and some oxygenated aliphatic compounds. Fig. 8 depicts the representative results for the saturated linear esters and ketones. Additional examples of CP-PC-SAFT’s predictions including inter alia the unsaturated and branched compounds can be found in the Supplementary Content (Figs. S2 and S3). As seen, this model is capable of particularly accurate predictions for these systems. At the same time, GC-PPC-SAFT tends to overestimate the solubility of CO2 in the liquid phases. Some hints probably explaining these results can be found in Fig. 8A depicting the critical loci of carbon dioxide – ethyl alkylate(2) systems. As seen, the overestimation of the pure compound critical points characteristic for GC-PPC-SAFT moves up also the binary critical loci, which apparently affects the subcritical VLE as well. Unsurprisingly, the effect of pure compound critical points on the high pressure phase equilibria increases in the cases of the more symmetric systems such as carbon dioxide(1) – dimethyl ether(2), diethyl ether(1) – 1-butanol(2) and 1-hexane(1) – 1-hexadecanol (Fig. 9A–C). As seen, the overestimation of the critical data notable affects the accuracy of GC-PPC-SAFT in the near-critical range. At the same time, the results of both models are nearly identical away from the critical states (see also Fig. 9D). And, finally, Fig. 10 depicts the representative examples of the low pressure phase equilibria. Since these phase equilibria are demarcated by the pure compound vapor pressures remote from the critical points, yet the advantage of GC-PPC-SAFT over CP-PCSAFT is obvious. As seen, the overestimation of the vapor pressure of the compounds such as n-alkanes, 1-dodecanol and butyl acetate (Fig. 10A and B) characteristic for CP-PC-SAFT leads to overestimation of their binary VLE as well. Unsurprisingly, the predictions of GC-PPC-SAFT for these data are nearly precise. At the same time, in the cases of substances such as dipropyl ether and 1-hexanol, whose pure compound vapor pressure data are decently estimated by CP-PC-SAFT in the entire temperature range, this model yields reasonable predictions of the low pressure VLE as well. Nevertheless even in such cases GC-PPC-SAFT apparently exhibits a better over-all accuracy (Fig. 10C). However a major advantage of GC-PPCSAFT is its outstanding potential in simultaneous predicting of VLE and LLE in symmetric systems [51]. Fig. 10D presents an example of this remarkable feature, namely the system n-heptane(1) – benzyl alcohol(2) at the atmospheric pressure. Although CP-PC-SAFT is also capable of qualitatively correct predicting the over-all picture of these phase equilibria, its quantitative performance is substantially less accurate. At the same time, it should be kept in mind that the GC-PPC-SAFT parameters for benzyl alcohol have been fitted, while CP-PC-SAFT appears here as an entirely predictive model. H. Lubarsky et al. / J. of Supercritical Fluids 115 (2016) 65–78 73 150 180 (a) P(bar) P(bar) (b) 39 3. 2 K 100 120 3.2 35 CO2 60 50 31 K K 3.2 0 0 300 400 500 T(K) 0.0 600 .2 .4 x1,y1 .6 .8 1.0 120 180 (d) (c) P(bar) P(bar) 80 120 3.2 39 K K .15 3 33 K 3.2 35 60 5K 3 .1 1 3 40 .2 K 313 0 0 0.0 .2 .4 x1,y1 .6 .8 0.0 1.0 150 .2 .4 x1,y1 .6 .8 1.0 .8 1.0 90 P(bar) (e) P(bar) 15 3. 5 3 100 K 60 5K 3.1 3 3 K .15 313 50 (f) 5 3.1 31 K 30 0 0 0.0 .2 .4 x1,y1 .6 .8 1.0 0.0 .2 .4 x1,y1 .6 Fig. 8. Phase equilibria in the systems of carbon dioxide(1). (a) the critical loci: 䊎 – ethyl acetate(2), - ethyl propionate(2), – ethyl butyrate(2). The isotherms: (b) propyl acetate(2), (c) butyl acetate(2), (d) ethyl butyrate(2), (e) 3-pentanone(2), (f) 2-hexanone(2). Points – experimental data [112–118]. Dashed lines − predictions of CP-PC-SAFT, solid lines – of GC-PPC-SAFT. 4. Conclusions In this study we have performed a comprehensive comparison between two SAFT approaches whose parameterization substantially diminishes referring to the experimental pure compound data, which radically increases their predictive values. In the case of CP-PC-SAFT, the only required information is the critical constants and triple point densities, which are available for large variety of compounds. Parameterization of GC-PPC-SAFT does not require any experimental information for the compounds comprised of the chemical groups included in its current parameter matrix. At the same time, implementation of this model to the first members of the homologues series of compounds and the branched molecules still requires fitting. In this study the models under consideration have been implemented to the mixtures of weakly- and non-associated oxygenated compounds, such as aromatic and aliphatic alkanols, esters, ethers and ketones in the entirely predictive manner, without adjusting any binary parameters. The considered data have included the available single phase thermodynamic properties in wide range of conditions, the existing information on the global phase behavior, the representative high pressure VLE in asymmetric and symmetric systems, and, finally, the characteristic low pressure phase equilibria data. 74 60 = K x1 39 74 0. 1 40 0.1 31 = 30 = 33 K (b) x 3 0.1 37 60 P(bar) 5K 8.6 5K 3.1 1 (a) x P(bar) 0. 47 65 90 28 8. 2 20 A 0 0 0.0 .2 .4 x1,y1 .6 .8 1.0 400 460 T(K) 520 580 27 60 P(bar) P(bar) (c) 3K 62 K 2.4 57 .4 K 524 40 20 (d) .15 453 K 18 15 K 423. K 393.15 9 K 472.1 373.15 K 0 0 0.0 .2 .4 x1,y1 .6 .8 1.0 0.0 .2 .4 x1,y1 .6 .8 1.0 Fig. 9. High pressure phase equilibria in symmetric systems. (a) carbon dioxide(1) – dimethyl ether(2), (b) diethyl ether(1) – 1-butanol(2), (c) n-hexane (1) – 1-hexadecanol(2), (d) n-pentane(1) – methyl benzoate(2). Points – experimental data [119–125]. Dashed lines – predictions of CP-PC-SAFT, solid lines − of GC-PPC-SAFT. H. Lubarsky et al. / J. of Supercritical Fluids 115 (2016) 65–78 30 H. Lubarsky et al. / J. of Supercritical Fluids 115 (2016) 65–78 75 420 600 (a) T (K) (b) T (K) 395 500 370 VLE 400 345 320 300 0.0 .2 .4 x1,y1 .6 .8 0.0 1.0 .2 .4 x1,y1 .6 .8 1.0 550 .3 P(bar) (c) 5K 3.1 32 (d) T(K) 450 .2 K .15 313 303.1 .1 VLE 5K 350 293.15 K LLE 250 0.0 0.0 .2 .4 x1,y1 .6 .8 1.0 0.0 .2 .4 x1 .6 .8 1.0 Fig. 10. Low pressure phase equilibria in symmetric systems. (a) n-hexane(1) – 1-dodecanol(2) at 1.013 bar, (b) n-hexane(1) – butyl acetate(2) at 1.013 bar, (c) dipropyl ether(1) – 1-hexanol(2), (d) n-heptane(1) – benzyl alcohol(2) at 1.013 bar. Points – experimental data [126–133]. Dashed lines – predictions of CP-PC-SAFT, solid lines – of GC-PPC-SAFT. The results indicate that both models under consideration are particularly accurate estimators of the single phase liquid densities at high pressures, typically with slight superiority of GC-PPC-SAFT. Although these results outline the universality of both approaches, this feature of CP-PC-SAFT can be considered as more advanced since this model yields accurate predictions also for sound velocities and compressibilities. No one of the considered approaches has exhibited a clear and over-all superiority in the case of phase equilibria. In this study we have considered the representative examples of VLE and LLE in various systems and conditions. The results indicate that GCPPC-SAFT is typically advantageous for the symmetric systems. This advantage is particularly pronounced at the low pressures since this model is a better estimator of pure compound vapor pressures away from the critical points. In addition, GC-PPC-SAFT is capable of particularly accurate estimations of the LLE in these systems. At the same time, unlike GC-PPC-SAFT, CP-PC-SAFT reproduces the experimental values of critical temperatures and pressures. Therefore the latter model is a more reliable estimator of the near-critical VLE, which probably supports its accuracy in predicting of the global phase behavior. Consequently, while exhibiting the less impressive over-all results for the symmetric systems, CP-PC-SAFT typically has a clear superiority in the cases of the asymmetric ones. In particular, unlike GC-PPC-SAFT, this model yields truthful predictions of the balance between LLE and VLE and more accurate estimations of solubility of gases in liquids under elevated pressures. At the same time, GC-PPC-SAFT can sometimes be advantageous in estimating the vapor phase compositions. The results also indicate that the more precise adjustment of both models under consideration to the data could not be achieved by a universal value of the binary parameter k12 . This is because in some cases positive, and in other negative values of this parameter are required. At the same time, predictive group-contribution methods for estimating these values for additional improvement of the precision of both models should be considered in future. Acknowledgements The authors would like to express their deepest thanks to Professor Dan Meyerstein for his fruitful discussion. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.supflu.2016.04. 013. References [1] I.G. Economou, J.-Ch. de Hemptinne, R. Dohrn, E. Hendriks, K. Keskinen, O. Baudouin, Industrial use of thermodynamics workshop: round table discussion on 8 July 2014. Meeting report, Chem. Eng. Res. Des. 92 (2014) 2795–2796. 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