Aspen Plus azeotropic distillation

The simulation is performed with the Radfrac module in ASPEN Plus and the NRTL liquid-activity model [20]. Tracing the RCM (Figure 3.15) shows that acetone and chloroform are unstable nodes, toluene is a stable node and the maximum-boiling azeotrope acetone-chloroform is a saddle. The distillation boundary shows a strong curvature. 

In Chapters, the steady-state design of a heterogeneous azeotropic distillation process for the dehydration of ethanol using benzene as a light entrainer was studied. The process consisted of two distillation columns, one decanter and two recycle streams. One of the recycle streams was successfully closed, but the second would not converge using steady-state Aspen Plus. 

Figure 8-14. Residue curves for water-ethanol-ethylene glycol for extractive distillation to break ethanol-water azeotrope. Curves generated by Aspen Plus 2004 using NRTL for VLE. Mass...

B. Explore. These components are in the Aspen Plus data bank and residue curves were generated with Aspen Plus using NRTL fFigure 11-111 (obviously, other process simulators could be used). Since there is one minimum boiling binary azeotrope between methanol (light component) and toluene (heavy) component without a distillation boundary, this residue curve map is similar to Figure 8-lla. We expect that the flowchart in either Figure 11-lQa or 11-1 Oh will do the separation. 

The vapor-liquid equilibrium (VLB) and liquid-liquid extraction (LLE) correlations in Aspen Plus are not always as accurate as possible. This can cause significant errors, particularly near pinch points in distillation columns. If data is available, Aspen Plus will find values of the parameters for any of the VLB or LLE correlations by doing a regression against the data you input. This is illustrated to obtain an improved fit for the non-random two-liquid (NRTL) VLB correlation for the binary system water and isopropanol (IPA). VLB data for water and isopropanol is listed in Table B-1. This system has a minimum boiling azeotrope at 80.46°C. The Aspen Plus fit to the data with NRTL is not terrible, but can be improved. 

The previous chapter discussed the methods and techniques for using Aspen Plus simulation software to develop and optimize steady-state designs for azeotropic distillation systems. Once the steady-state design is complete, the dynamic controllability of the process should be explored. Only looking at the steady state does not tell you whether the process is operable. Dynamic simulations and the development of an effective control stmcture are vital parts of process development. 

Most of the treatments in the above books are qualitative and concepmal in namre, emphasizing VLLE issues and alternative configurations. Few of these books present in-depth rigorous designs that achieve optimum economic criteria. None of these books deal with the control and operation of azeotropic distillation systems. Detailed discussions of these two areas are the main contribution of this book. Rigorous steady-state and dynamic simulation tools (Aspen Plus and Aspen Dynamics) are used for design calculations and rigorous dynamic simulations. 

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