4.2 Simulation results of a rectification process for each of the studied dissolutions

The models obtained previously are used in the design of a simulation operation comparing their capacity in terms of some operation variables such as composition and temperature profiles, as well as energy consumption. General conditions for the simulations are summarized in Table 4. In all cases, columns are fed with a 1 kmol/h at equimolar composition of the corresponding solution, at 298.15 K and 101.32 kPa. Simulations are performed using the RadFrac block of AspenPlus© V8.8 (AspenOne©, [59]).

## Figure 11.

produces a quasi-linear behavior with the variation of s(h<sup>E</sup>

) at 170 J mol<sup>1</sup> and 450 J mol<sup>1</sup>

either result 2 or 3 is discouraged since their estimations of h<sup>E</sup>

E

models M1 and M2 do not intersect, unlike the earlier case, showing a maximum

produced by the four selected results are shown in Figure 10, along with one of the validated data series for this result. The best description of this system is achieved with result 4 (M1), which reproduces the behavior of T-x-y experimental data (Figure 10(a)) and the other quantities calculated (Figure 10(b and c)). Nevertheless, the description of h<sup>E</sup> with this model is not good. Result 1 (M2) produces an azeotrope at x<sup>1</sup> < 0.2, which does not occur experimentally. This poor estimation occurs even though the greater number of parameters, increasing the model's

This discrepancy gives rise to the formation of minimum boiling point azeotropes, which are not in accordance with experimental data. Of all the results chosen, only result 1 (belonging to sub-model M2) shows a h<sup>E</sup> that varies significantly with temperature, since sub-model M1 is independent of this variable. The use of

atures other than 298 K, are not correct, in addition to the described issues in

Plot of VLE at 101 kPa estimates for binary benzene(1) + hexane(2). Models drawn from Figure 9. Results (——) 1 (M2), 2 (M1), 3 (M1) and 4 (M1). (a) T vs x,y; (b)γ vs x; (c) gE

this front and that of sub-model M2 is δs(g

Distillation - Modelling, Simulation and Optimization

/RT (see Figure 10(b and c)).

value of s(h<sup>E</sup>

hence g E

Figure 10.

60

capacity to reproduce the h<sup>E</sup>

). The difference between

, especially at temper-

/RT vs x.

/RT) ≈ 0.14, when ε = 0. The fronts for

, respectively. The VLE diagrams

, as proven in Figure 11. Results 2 and 3 overestimate γi,

Estimation of hE values at 101.32 kPa using the different results indicated in the fronts of Figure 9 for benzene (1) + hexane(2). (a) hE vs x1 (T = 298.15 K), (b) hE vs T (x1 = 0.5). Results (——) 1 (M2); 2 (M1); 3 (M1); 4 (M1).


## Table 3.

List of sub-models applied to each system.


## Table 4.

Operation data for the rectification columns to separate the binaries.

Acetone(1) + ethanol(2): the simulation of a rectification column to purify the acetone+ethanol binary system, using the result labeled as "2" in Figure 7, does not provide a coherent resolution because it estimates the presence of two immiscible liquid phases. The final values obtained with results 1 and 3 are detailed in Table 5, while the composition profiles are shown in Figure 12. In both cases the composition of the distillate is higher than 99% in acetone and at the same temperature in the stage.

The composition profiles and temperature gradient of the two tested solutions present similar qualitative behaviors. Most of the column is used as an enriching

A Practical Fitting Method Involving a Trade-Off Decision in the Parametrization Procedure…

Benzene(1) + hexane(2): values obtained in the simulation of the distillation operation of this binary dissolution are in Table 6, while composition and temperature profiles are plotted in Figure 13. For the first three results (1, 2, and 3), the presence of an azeotrope limits the distillate composition. Thus, result 1 produces an effluent with a benzene composition of 16.7% (v/v), while for results 2 and 3, the compositions are, respectively, 37.2 and 30.9%. The simulation carried out with the parametrization of result 4 produces a purer distillate of 15.6%, due to the absence of the azeotrope. However, the folding effect observed between the equilibrium curves in experimental data as well as the diagram estimated by result 4 complicates the separation beyond this point. This justifies that the composition profiles are

The residual streams obtained by results 1 and 4 contain benzene with a purity higher than 99.9%, while the other two results do not produce the separation of the

1 0.167 0.161 341.3 0.372 0.372 337.3 0.310 0.309 340.1 0.167 0.156 341.7 5 0.201 0.189 341.3 0.372 0.372 337.3 0.312 0.311 340.1 0.220 0.202 341.9 10 0.280 0.250 341.6 0.372 0.372 337.3 0.319 0.316 340.1 0.310 0.278 342.2 15 0.505 0.414 343.1 0.374 0.373 337.3 0.337 0.330 340.1 0.473 0.407 343.2 20 0.842 0.740 348.5 0.405 0.388 337.4 0.392 0.369 340.2 0.772 0.663 346.8 25 0.991 0.982 352.6 0.409 0.390 337.4 0.422 0.389 340.3 0.988 0.975 352.4 30 1.000 0.999 352.8 0.692 0.510 338.8 0.785 0.631 344.0 1.000 0.999 352.8 Qc/kJ h<sup>1</sup> 1.829E5 1.988E5 1.686E5 1.804E5 Qr/kJ h<sup>1</sup> 1.886E5 2.050E5 1.802E5 1.898E5

Quantities obtained in the simulation of a distillation process for the binary benzene(1) + hexane(2), using

Plot of composition and temperature profiles obtained in the simulation of a separation operation for the binary benzene(1) + hexane(2), using the different parametrizations proposed: (——) 1 (M2); (- - - -) 2 (M1);

x<sup>1</sup> y<sup>1</sup> T/K x<sup>1</sup> y<sup>1</sup> T/K x<sup>1</sup> y<sup>1</sup> T/K x<sup>1</sup> y<sup>1</sup> T/K

Stage Result 1 (M2) Result 2 (M1) Result 3 (M1) Result 4 (M1)

region which requires a high number of stages in both cases.

similar to results 1 and 4 (see Figure 13).

DOI: http://dx.doi.org/10.5772/intechopen.85743

different values from the efficient front shown in Figure 9.

() 4 (M1). L, liquid stream profile; V, vapor stream profile.

Table 6.

Figure 13.

63

The exact purity is slightly higher with result 1 than with result 3, the difference being 0.2%. The calculation in the bottoms of the tower reveals differences between the two parametrizations, giving place to an effluent somewhat purer in the case of result 1. The difference between both models is 0.001 in molar fraction. These observations directly affect the calculation of the energy balance and, therefore, to the consumed energy. Thus, the consumption in the condenser is estimated similarly with both parametrizations, while that of the reboiler is significantly higher with result 3, due to the greater quantity of ethanol and the incorrect estimate of other quantities, such as the mixing enthalpies.


## Table 5.

Quantities obtained in the simulation of a separation process for the binary acetone(1) + ethanol(2), using different values from the efficient front shown in Figure 7.

## Figure 12.

Plot of composition and temperature profiles obtained in the simulation of a separation operation for acetone (1) + ethanol(2) system, using the different parametrizations proposed: (—) 1 (M4). L, liquid stream profile; V, vapor stream profile.

A Practical Fitting Method Involving a Trade-Off Decision in the Parametrization Procedure… DOI: http://dx.doi.org/10.5772/intechopen.85743

The composition profiles and temperature gradient of the two tested solutions present similar qualitative behaviors. Most of the column is used as an enriching region which requires a high number of stages in both cases.

Benzene(1) + hexane(2): values obtained in the simulation of the distillation operation of this binary dissolution are in Table 6, while composition and temperature profiles are plotted in Figure 13. For the first three results (1, 2, and 3), the presence of an azeotrope limits the distillate composition. Thus, result 1 produces an effluent with a benzene composition of 16.7% (v/v), while for results 2 and 3, the compositions are, respectively, 37.2 and 30.9%. The simulation carried out with the parametrization of result 4 produces a purer distillate of 15.6%, due to the absence of the azeotrope. However, the folding effect observed between the equilibrium curves in experimental data as well as the diagram estimated by result 4 complicates the separation beyond this point. This justifies that the composition profiles are similar to results 1 and 4 (see Figure 13).

The residual streams obtained by results 1 and 4 contain benzene with a purity higher than 99.9%, while the other two results do not produce the separation of the

