https://doi.org/10.3389/fenrg.2021.785039
“The data from experiments and the literature were regressed in this model, including excess enthalpy, the VLE data acquired in this study, and heat capacity (Poozesh et al., 2013; Tagiuri, 2019) for the mixed solution of HEPZ/H2O. The pKapKa values were obtained by regression through manual adjustment of the standard-state properties of HEPZH+HEPZH+ and HEPZH2+HEPZH2+. The regressed parameters along with their standard deviations are shown in Table 3.”
“TABLE 3. Parameters regressed for HEPZ/H2O and their deviations (α= 0.3α= 0.3).”
“In this study, VLE data at 30 kPa, 40 kPa, 55 kPa, 70 kPa, and 85 kPa and the atmosphere pressure of 101 kPa were measured. Because the viscosity of the high-concentration solution of HEPZ is too large, it is not convenient for experimental measurements. The mass fraction range of HEPZ in this experiment is 0.1–0.75. Figure 3 shows the data obtained by the experimental measurement and the data calculated by the model. The upper line and points represent for the mole fraction of HEPZ at the gas phase (yHEPZyHEPZ), and the lower ones stand for the mole fraction of HEPZ at the liquid phase (xHEPZxHEPZ). Because the solution will turn yellow at high temperature, there will be certain errors in the analysis with a refractometer. Besides, the boiling point of HEPZ is much higher than that of H2O, and the concentration of HEPZ in the gas phase distilled from the HEPZ solution in this study is very low, resulting in a larger measurement error. The average relative deviation of the VLE data xHEPZ xHEPZ /yHEPZyHEPZ of HEPZ at negative pressure is 1.66%/70.9%, 1.26%/57.7%, 0.294%/46.7%, 0.0519%/8.17%, and 0.529%/153%, respectively. The average relative deviation of the VLE data xHEPZ xHEPZ /yHEPZyHEPZ of HEPZ at atmosphere pressure is 0.760%/57.2%.”
“FIGURE 3. VLE data for HEPZ/H2O at 30 kPa, 40 kPa, 55 kPa, 70 kPa, 85 kPa, and 101 kPa. (A) Gas-phase data; (B) liquid-phase data: lines, Aspen results: blue, 30 kPa; yellow: 40 kPa; gray: 55 kPa; red: 70 kPa; green: 85 kPa; and black: 101 kPa; points, this study: ●, 30 kPa; ■, 40 kPa; □, 55 kPa; ▲, 70 kPa; ○, 85 kPa; and ◆: 101 kPa.”
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HEPZ has two dissociation constants pKa1 and pKa2, which are regressed by the manual adjustment of the standard-state properties of HEPZH+HEPZH+ and HEPZH2+HEPZH2+, with the standard formation Gibbs Free Energy at 298.15 K ΔfG∞,aq298.15KΔfG298.15K∞,aq, the standard enthalpy of formation at 298.15 K ΔfH∞,aq298.15KΔfH298.15K∞,aq, and the infinite dilution state heat capacity parameter at 298.15 K C∞,aqpCp∞,aq. The non-randomness factor αα was a fixed value (0.3), and the results of these properties are listed in Table 3. The average value of the relative deviation between the pKa1 and pKa2 data from the study by Hamborg and Versteeg (2009) and Aspen is 0.01%.
Poozesh et al. (2015) and Tagiuri (2019) measured the heat capacity values for HEPZ/H2O at various temperatures ranging from 303 to 353 K, and the mole fraction of HEPZ ranges from 0.1 to 0.9. In Figure 4, the calculated value of the model is compared with the measured value of the literature. In the high-concentration area, Figure 5 shows that there is a good correlation between the value calculated by Aspen and the experiment values. However, in the area of low concentration, the experiment values increase as T increases, and the calculated values do not show the same trend. The average relative deviation of all points is 0.0235%. The excess enthalpy of HEPZ/H2O calculated by Aspen is shown in Figure 5, and the average value of the relative deviation for excess enthalpy regression was 8.57%.”
“FIGURE 4. Heat capacity values for HEPZ/H2O (lines: Aspen, this study; points: ●: x=0.1002x=0.1002; ●: x=0.2006x=0.2006; ●: x=0.3x=0.3; ●: x=0.4044x=0.4044; ●: x=0.5x=0.5; ●: x=0.6012x=0.6012; ●: x=0.7x=0.7; ●: x=0.8x=0.8; and ●: x=0.9x=0.9).”
“FIGURE 5. Excess enthalpy of HEPZ/H2O.”