Comparison of Three Candidate Entrainers

Three candidate acetates will be studied in detailed process simulations to demonstrate the factors needed to be considered in determining the suitable entrainer for this system. The three candidate acetates to be considered are ethyl acetate (Tanaka and Yamada and Siirola ), isobutyl acetate (iBuAc) (Costantini et al. and Patten and Ure ), and w-butyl acetate (Othmer °). The important experimental physical properties of these three acetates at atmospheric pressure are listed in Table 9.1. The azeotropic data are from Horsley and Gmehling, the VLB data are from Gmehling and Onken, with the VLB data for acetic acid-isobutyl acetate system from Christensen and Olson. The binary and ternary BBB data are from Sprensen and Arlt.  

The NRTB activity coefficient model (Renon and Prausnitz ) was used for the VBBB for the ternary system. The Hayden-O Connell second virial coefficient model, with association parameters, was used to account for the dimerization of acetic acid in the vapor phase. The Aspen Plus built-in association parameters were employed to compute ffigacity coef-hcients. The extended Antoine equation is used to calculate the vapor pressure of each component in the system. The Aspen Plus built-in parameters were again used in the simulation. 

The set of NRTB parameters used provides a good match between predicted and experimental data binary and ternary VBB and BBB. The sets of NRTB parameters for the ternary systems of acetic acid-water-ethyl acetate, acetic acid-water-isobutyl acetate, and acetic acid-water-M-butyl acetate are listed in Tables 9.2 to 9.4. The NRTB model parameters are obtained by htting all binary and ternary VBB and BBB data while trying to get a good prediction of the azeotropic temperature and composition. The pure component parameters used in the Hayden-O Connell model are shown in Table 9.5 while the association parameters 

Acetate Normal Boiling Point (°C) Azeotropic Component Azeotropic Temp. (°C) Azeotropic Composition (Water, mol%) Aqueous Phase (Acetate, mol%) Organic Phase (Acetate, mol%) 

ACETIC ACID-WATER (ISOBUTYL ACETATE AS THE ENTRAINER) 

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In Chapter 9, three candidate acetates were studied in detailed process simulations to determine the best entrainer for this system. The three candidate acetates considered were ethyl acetate, isobutyl acetate, and n-butyl acetate. Rigorous process simulations were performed to find the optimum design and operating conditions of these three entrainer systems. In each entrainer system, the total annual cost (TAC) was used as the objective function to be minimized. From a comparison of the minimized TAC, the isobutyl acetate was selected as the best entrainer with the lowest TAC and operating utility cost. 

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