3.4 Results and discussion
3.4.3 Results of density measurement
To validate the experimental procedure of the measurement, the densities of pure MDEA and mass percentages of 10 %, 20 % and 30% MDEA aqueous solutions were measured at 288 K, 313 K and 333 K and compared with the values reported by Al-Ghawas et al. [8] and
Maham et al. [51]. These are presented in Table 3.13. The average absolute deviations (AAD) of the density measurements are 0.15 %, 0.05 %, 0.07 % and 0.13 % for pure MDEA and 10
%, 20 % and 30% MDEA aqueous solutions, respectively. Thus, the density data obtained in this study are in good agreement with the data of Al-Ghawas et al. [8] and Maham et al. [51].
The measured densities of different binary and ternary aqueous solutions are presented in Figures 3.12 – 3.19 (also presented in Tables III.9 – III.16 of Appendix III). As the densities of 2-PE and MEA are very close to each other the variations in the densities of (2-PE + MEA + H2O) system with different amine compositions are insignificant. The densities of this ternary system increase slightly with increase in concentrations of MEA in the blends. So, the densities of (2-PE + MEA + H2O) system cannot be distinctly represented by figure for which the density of this system is shown in tables (Table 3.15). For single amine solutions the density increases with the increase in amine concentrations in the solutions. For blends of (2PE + DEA) the density increases with the increase in DEA concentration in the blends (Figure 3.15). In case of blends of PZ or PZEA with the other alkanolamines, densities increase with increase in PZ or PZEA concentrations (Figures 3.16 – 3.19).
The density measurements of this study are in good agreement with the literature results.
The figures and tables also show the comparison between the literature resultsand the results obtained in this study wherever applicable (Table 3.15, Figures 3.12 and 3.13). For the aqueous solution of 10 mass % 2-PE over the temperatures of 298 K and 323 K, the experimental data of this study show 0.09 % deviation from the experimental data of Xu et al.
[11]. For the aqueous solution of 30 mass % 2-PE over the temperatures of 298 K and 323 K, the experimental data of this study show 0.08 % deviations from the experimental data of Xu et al. [11]. For the amine blends of 2-PE and MEA like (w1 = 6 % and w2 = 24 %), (w1 = 12 % and w2 = 18 %), (w1 = 18 % and w2 = 12 %), and (w1 = 24 % and w2 = 6 %) over the temperatures of 303 K, 313 K, 323 K and 333 K, the experimental data of this study show 0.03 %, 0.06 %, 0.10 %, and 0.17 % deviations, respectively, from the experimental data of Hsu and Li. [49]. For the aqueous solution of 10.3 mass % AHPD over the temperatures of 298 – 313 K, the experimental density data of this study show 0.18 % deviation from the experimental data of Tourneux et al. [44]. For the aqueous solution of 5.10 – 15.8 mass %
AHPD over the temperatures of 303 – 323 K, the experimental density results of this study show 0.32 % deviation from the experimental data of Park et al. [59].
Different correlations are used to correlate the experimental data as function of temperature and amine concentration depending on the nature of the data. To correlate the densities of (2-PE + H2O), (PZEA + H2O), (2-PE + MEA + H2O), (2-PE + DEA + H2O) and (PZEA + MDEA + H2O) a Redlich-Kister type equation for the excess molar volume is applied which has the following expression [49, 56]:
( )
0
= -
n i
E
jk j k i j k
i
V x x A x x
∑
= (3.15)where Ai are pair parameters and are assumed to be temperature dependent as follows:
2
Ai = +a bT+cT (3.16)
The excess volume of liquid mixtures for the binary system is assumed to be
12
E E
V =V (3.17)
The excess volume of liquid mixtures for the ternary system is assumed to be
12 23 13
E E E E
V =V +V +V (3.18)
The excess volume of liquid mixtures can be calculated from the measured density of the fluids
- 0 E
m i i
V =V
∑
x V (3.19)where Vm is the molar volume of the liquid mixture and Vi0
is the molar volume of the pure fluids at the system temperature. The molar volume of the liquid mixtures is calculated by
i i m
m
V x M
=
∑
ρ (3.20)where Mi is the molar mass of pure component i, ρmis the measured liquid density and xi is the mol fraction of the pure component i.
A general set of temperature-dependent parameters has been developed using experimental data. The determined parameters are presented in Tables 3.16 – 3.19. The densities of the pure 2-PE, MEA and DEA have been taken from the literature [49]. The
density of pure PZEA has been measured and correlated as a function of temperature using the following correlation:
4 2
1159.7 0.4128T 5.9431 10 T
ρ= − − × − (3.21)
As PZ is solid in the temperature range of 288 – 333 K it is not possible to find out the viscosity variation of pure PZ with temperature. So, for (PZ + MDEA + H2O), (PZ + AMP + H2O) and (PZ + 2-PE + H2O) systems the molar volume rather than the excess volume of the liquid mixtures are correlated using the following expression:
12 23 13
m m m m
V =V +V +V (3.22)
where
( )
0
= -
n i
jk
m j k i j k
i
V x x A x x
∑
= (3.23)where Ai are the temperature dependent pair parameters and expressed by Eq. (3.16). The temperature-dependent parameters developed using experimental data are presented in Table 3.20 – 3.22.
AHPD is also solid in the temperature range of 298 – 323 K. But Eq. (3.22) is unable to predict the experimental density data for (AHPD + H2O) systems with appreciable accuracy.
So, the densities of (AHPD + H2O) systems are correlated as a function of amine concentration and temperature using the following polynomial equation:
( )
2
2 0
i i i
i i i
i
A x B x T C x T ρ
=
=
∑
+ + (3.24)where x is the mole fraction of AHPD in the solutions. The determined parameters for density and viscosity are obtained by regression analysis of the experimental data of this work and are presented in Table 3.23.
The calculated densities from the different correlations are in excellent agreement with the experimental data. The measured and calculated densities from the correlations for different binary and ternary systems are compared in Figures 3.12 – 3.19.