THERMOPHYSICAL PROPERTIES OF AQUEOUS SINGLE AND BLENDED AMINES
3.3 Results and discussion
3.3.1 Measurement and correlation of density
For the validation of the experimental methodology adopted in the present system for density measurements, the densities of (0.10, 0.20 and 0.30) mass fraction aqueous MDEA were measured from (303.2 to 333.2) K and the experimental results were compared with the literature
data [6, 12]. These comparisons are reported in Table 3.2. The average absolute deviations (%
AAD) of the density data are 0.07, 0.04 and 0.07 for the amine solution having the composition of (0.10, 0.20 and 0.30) mass fraction of MDEA, respectively. The low AAD value indicates that the experimental results are in excellent agreement with the literature data. The experimentally measured density values of aqueous binary and ternary solution were evaluated by varying the temperature from (303.2 to 343.2) K. These are reported in Tables 3.3-3.8 and elsewhere [40 – 41].
The experimental density data measured in this work has been further correlated using the Redlich- Kister type equation as suggested by Paul et al. [42]. A semi-empirical Redlich-Kister equation was used to determine the excess properties of amine solutions like excess molar volume as a function of molar composition. The Redlich-Kister equation can be expressed as:
0
( )
N
E p
jk j k p j k
p
V x x A x x
(3.1)In equation (3.1), VEis the excess molar volume of the amine mixture,xjandxkare the mole fraction of the pure components in the amine mixture,Apis the optimized pair parameter and N represents total number of optimized pair parameters. The temperature dependency of the pair parameter can be expressed in terms of temperature dependent coefficients l m, and n respectively:
. . 2
Ap l m Tn T (3.2) For the binary system, the excess volume is then calculated using equation (3.3).
E12
E V
V (3.3) For the ternary system, the excess volume is calculated from the individual contributions as expressed below.
23 13
12 E E
E
E V V V
V (3.4)
Further the experimental measured density is used to determine the excess volume of the amine solution
m i io
E V xV
V (3.5)
Where, Vio
and Vm represents the volume of the pure constituent and amine mixture at a specified temperature in molar scale. Vm is then calculated from the experimental measured density by
(3.6)
Where, Mi represents the molar mass of pure constituenti, m corresponds to the experimentally calculated density of the amine mixture, and xi represents the mole fraction of the pure constituenti.
The temperature dependent binary interaction parameters of equation (3.2) for the amine mixtures have been calculated by regression of experimental data within the temperature range of (303.2 to 343.2) K and are reported in Tables 3.9-3.14. The pure component densities of all the constituents used in the present work can be obtained from various literature sources [12, 37, 43 - 44] but pure component density of AEP over the experimental temperature range were determined experimentally in the present work and reported elsewhere [40] as this data is not available in the open literature. The % (AAD) between the correlated and experimental results are determined by using equation (3.7)
, exp,
1 exp,
% 1 100
N cal i i
i i
X X
AAD N X
(3.7)
Where N is the total number of data points, Xcal i, and Xexp,i represents the correlated and experimental results. The % (AAD) between the experimental and correlated results for (AEP + H2O) as well as (AEP + MDEA + H2O) and (AEP + AMP + H2O) systems are 0.04, 0.04 and
m i i m
M V x
0.08, respectively. Whereas binary and ternary system of (APDA + H2O), (APDA + MDEA + H2O) and (APDA+ AMP + H2O) shows an average absolute deviation of 0.06, 0.07 and 0.05, respectively. The lower values of AAD across all the solvent systems studied in this work indicate that experimental results are in well agreement with the model calculated data. The comparison between the correlated and experimental results is represented in Figs. 3.1 - 3.6.
It shows a decreasing trend in the measured density with increase in temperature since the volume of solution increases. Excess volume of the amine mixtures can be calculated using equation (3.5) and it is compared with the model calculated value. The excess volume (VE) for the binary mixture of (AEP + H2O) shows negative value for all the composition and temperature range studied. While for the (AEP+ MDEA/AMP +H2O), the VE shows positive sign. The sign convention for the excess volume can be analyzed on the basis of three kinds of interactions between the individual constituent of a solution [45] forces resulting in +ve contribution, (b) –ve contribution can be the results of various kinds of chemical interactions such as charge transfer, the formation of H-bonds and other complex interactions (c) variation in size and shape of the individual component of the mixtures, results in structural variation and due to the random packing of molecules into each other’s structure leads to the reduction of the overall molar volume and compressibility of the solution mixtures, which also results in a – ve value of VE. The –ve excess value of the binary system understudied reflects strong interactions among unlike molecules. Taking into account the sign and magnitude of VE, It can be inferred that there are strong interactions such as hydrogen bonding prevailing in the blends [25].
Fig. 3.1 Density of aqueous AEP system at various temperatures and composition (mass fraction)
Fig. 3.2 Density of aqueous APDA system at various temperatures and composition (mass fraction)
Fig. 3.3 Density of aqueous (AEP + MDEA) system at various temperatures and composition (mass fraction)
Fig. 3.4 Density of aqueous (AEP + AMP) system at various temperatures and composition (mass fraction)
Fig. 3.5 Density of aqueous (APDA + MDEA) system at various temperatures and composition (mass fraction)
Fig. 3.6 Density of aqueous (APDA + AMP) system at various temperatures and composition (mass fraction )