Some Aspects of Phase
Equilibria Behavior and
Verification
10
CONTENTS
10.1 Introduction ..................................................................................................... 113
10.2 Discussion and Results .................................................................................... 114
10.3 Conclusion ....................................................................................................... 118
Keywords ................................................................................................................. 119
References ................................................................................................................ 119
10.1 INTRODUCTION
Liquid-liquid equilibrium data are essential for the comprehension of extraction pro-
cess, and solvent capacity, solubility, selectivity, and other extraction variable can be
estimated from these data. The efficient separation of organic acids and alcohols from
aqueous solution is an important subject in chemical fermentation industries and many
solvent have been used to improve the recovery processes [1, 2].
The phase behavior experimental data for (water + carboxylic acid + 1-octanol)
and (water + carboxylic acid or alcohol +1-hexanol) systems were reported by Senol
[3, 4]. Letcher and Redhi [5] studied the phase behavior of (butanenitrile + a carbox-
ylic acid + water) systems and Bilgin et al. [6] tested the ternary system behavior of
(water + propionic acid + alcohol) systems.
Certain liquid-liquid equilibrium data of the ternary systems were also investigated
by non-random two liquid (NRTL) [7], universal quasi chemical theory (UNIQUAC)
[8], universal functional group activity coef cient (UNIFAC) [9], Dortmund modi ed
UNIFAC [10] models. The experimental data [3, 4] were used in order to analysis the
liquid-liquid equilibrium behavior in this chapter. The experimental data [3, 4] were
compared with Aspen Plus 11.1.
The main purpose of this chapter is to verify the phase equilibria behavior for
ternary liquid systems, using different models. The NRTL [7] models for strongly
non-ideal mixture, and especially for partially immiscible systems, the NRTL equation
often provides a good representation of experimental data if the adjustable parameters
obtained by enough attention using experimental data. The UNIQUAC [8] equation
is applicable to a wide variety of non-electrolyte liquid mixture containing non-polar
114 Advanced Process Control and Simulation for Chemical Engineers
or polar uids such as hydrocarbons, alcohols, nitriles, ketones, aldehydes, organic
acid, and water including partially miscible mixture. With only two adjustable binary
parameters, it cannot always represent high quality data with high accuracy, but for
many typical mixtures encountered in chemical practice, UNIQUAC provides a satis-
factory description.
The UNIFAC [9] activity coef cient model is an extension of the UNIQUAC
model. It applies the same theory to functional groups that UNIQUAC uses for mol-
ecules. A limited number of functional groups are suf cient to form an in nite num-
ber of different molecules. Group-group interactions determined from a limited, well
chosen set of experimental data are suf
cient to predict activity coef cients between
almost any pair of components. The UNIFAC (Fredenslund et al., 1975, 1977) can be
used to predict activity coef cients for VLE. For LLE a different dataset must be used.
Mixture enthalpies, derived from the activity coef cients are not accurate. This model
can be applied to VLE, LLE, and enthalpies (Larsen et al., 1987). Another UNIFAC
modi cation comes from the University of Dortmund (Germany). This modi cation
is similar to Lyngby modi ed UNIFAC, but it can also predict activity coef cients at
in nite dilution (Weidlich and Gmehling, 1987). The UNIFAC modi cation by Gmehling
and coworkers (Gmehling et al., 1993, Weidlich and Gmehling, 1987), is slightly dif-
ferent in the combinatorial part [10].
10.2 DISCUSSION AND RESULTS
The compositions of experimental data for the ternary mixtures of (water + acetic
acid +1-hexanol) and (water + acetic acid + 1-octanol) obtained at T = 293.15K,
atmospheric pressure are shown in Tables 1 and 2 [3, 4]. The corresponding tri-
angular diagrams for the ternary mixtures of (water + acetic acid +1-hexanol) and
(water + acetic acid + 1-octanol) are presented in Figures 1, 2, 3, and 4. The NRTL,
UNIQUAC, UNIFAC, and Dortmund modified UNIFAC equations of state were
used in order to compare with the experimental data. The comparison between
calculated and experimental compositions (water + acetic acid +1-hexanol) can be
seen in Figures 1 and 2.
TABLE 1 Experimental data compositions (mass fraction) at T = 293.15K
[3].
Water-rich 1-hexanol-rich
w
1
w
2
w
1
w
2
Water (1) + Acetic acid (2) + 1-hexanol (3)
0.9922 0 0.0305 0
0.9624 0.0296 0.0383 0.0198
0.9022 0.0889 0.0514 0.0648
0.8553 0.1345 0.0705 0.1032

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