9.2 Sensitivity analysis of methyl acetate RDC

Reactive distillation exhibits multiple steady-state conditions throughout the operation. This is known as multiplicity of the process. There are two types of multiplicity; one is known as input multiplicity, and the other is known as output multiplicity. This is the condition in which column gives same output for the different sets of process condition. In this paper, we have studied input multiplicity, in which we obtained same output for different input conditions. To analyze the situation, we have performed sensitivity analysis in Aspen Plus simulator.

For sensitivity analysis, we have first chosen molar flow of methyl acetate on the basis of heat duties whose lower and upper bounds are fixed as 1 and 3 kW, respectively. For the second case, we have calculated mass fraction of methyl acetate by

Figure 8. Temperature profile of methyl acetate RDC.

9.3 Optimization of methyl acetate RDC

Reactive Distillation: Modeling, Simulation, and Optimization

DOI: http://dx.doi.org/10.5772/intechopen.85433

Sensitivity analysis based on acid flow rate.

Row Case I

Variation in reboiler heat duty Btu/hr

Summary of the sensitivity and optimization results.

Figure 10.

Table 5.

105

Model analysis tool under Aspen Plus simulation facilitates optimization of the reactive distillation column. In this analysis we defined mass fraction of methyl acetate as objective on the basis of standard volumetric flow rate of acetic acid to obtain the minimum product composition that can be achieved at the top of the column. Heat duty was defined as constraint with fixed values between 1 and 3 kW

> Case II Variation in volumetric flow rate of acetic acid, ft<sup>3</sup>

> > hr

/

Optimized product composition

Optimized flow rate of methyl acetate lbmol/hr

 3412.14 0.0549 0.0211 0.4808 4170.39 0.0637 0.0376 0.6776 4928.64 0.0723 0.05414 0.8070 5686.90 0.0807 0.07062 0.9011 6445.15 0.0888 0.08710 0.9522 6824.28 0.0926 0.10358 0.9596 7203.41 0.0920 0.10594 0.9604 7961.66 0.0904 0.12006 0.9643 8719.91 0.0902 0.13655 0.9676 9478.17 0.0900 0.15303 0.9700 11 10236.42 0.0893 0.16951 0.9719

Figure 9. Sensitivity analysis based on reboiler heat duty.

setting the molar flow of acetic acid in feed in the range of 0.01–0.08 L/min. In the third case, we have calculated distillate flow rate by varying feed flow rate in the range of 0.01–0.08 L/min to calculate the distillate-to-feed ratio (D/F). Similarly we have also calculated bottom-to-feed ratio (B/F). The result curves are shown in Figures 9 and 10, respectively. A shown in Figure 9, we can observe that the flow rate of methyl acetate is increasing as heat duty is increasing and found the maximum flow rate to be 0.927 lbmol/hr. at heat duty of 6820 Btu/hr. Similarly, we can observe that in Figure 10, the variation in flow rate of acetic acid is observed WRT mole fraction of product methyl acetate. The maximum product fraction is observed as 95.2% at flow rate of 0.0872 cuft/hr. The effect of change in distillate-to-feed Ratio (D/F) and change in bottom-to-feed (B/F) ratio on composition was also observed. It was found that optimized distillate-to-feed (D/F) ratio obtained 0.6275 and optimized bottom-to-feed (B/F) ratio obtained 0.4238 to get maximum product purity.

Reactive Distillation: Modeling, Simulation, and Optimization DOI: http://dx.doi.org/10.5772/intechopen.85433

Figure 10. Sensitivity analysis based on acid flow rate.
