Residue Curve Mapping Technique

The RCM technique has been considered a powerful tool for the flowsheet development and preliminary design of conventional multicomponent, nonideal separation processes (Fien and Liu, 1994). It represents a good approximation to actual equilibrium behavior and allows the designer to perform feasibility analysis of separation processes where nonideal and azeotropic mixtures are involved. Traditionally, nonreactive residue curves have been used to predict the liquid-composition trajectories in continuous distillation 

Analytically, ROMs are constructed based on physical properties of the system (ie. VL equilibrium, LL equilibrium and solubility data), wherein the composition of a nonreacting liquid remaining in the system (figure 5.1) may be determined by performing an overall and component material balances in the system (Westerberg et al., 2000), 

Combining the previous n-l ] independent expressions 5.3 with and appropriate vapor-hquid equilibrium model enables to define the set of simultaneous equations that describe the residue curves, dxi 

When a mixture of nc-components undergoes rirx simultaneous equilibrium chemical reactions, the RCM expression may be described in terms of transformed molar compositions and a reaction-warped time (Ung and Doherty, 1995a), 

From the above-mentioned expressions it can be inferred that, 

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Answer. Improved residue curve mapping technique, multilevel modeling approach, dynamic optimization of spatial and control structures, steady-state and dynamic behavior analysis, generic lumped reactive distillation volume element, multiobjective optimization criteria. 

An ideal mixture of n components requires a sequence of n - 1 conventional distillation columns (two product streams) to separate the components completely. The columns can be arranged sequentially without recycle between them. This picture changes when mixtures forming azeotropes must be separated. Nonideal systems sometimes require complex distillation arrangements involving more than n - 1 columns with recycle of material between the columns. For the analysis of such systems, we recommend the use of residue curve maps. We base the following summary on the excellent book by Doherty and Malone (1998), who pioneered the use of these techniques. 

We start the chapter by explaining the graphical thermodynamic representations for ternary mixtures known as Residue Curve Maps. The next section deals with the separation of homogeneous azeotropes, where the existence of a distillation boundary is a serious obstacle to separation. Therefore, the choice of the entrainer is essential. We discuss some design issues, as entrainer ratio, optimum energy requirements and finite reflux effects. The following subchapter treats the heterogeneous azeotropic distillation, where liquid-liquid split is a powerful method to overcome the constraint of a distillation boundary. Finally, we will present the combination of distillation with other separation techniques, as extraction or membranes. 

The example presented in this section is a condensed version of a study detailed in the book Membrane Process Design Using Residue Curve Maps [1] and has been reproduced with permission from John Wiley Sons, Inc. The example is included here to demonstrate the versatility and adaptability of the techniques discussed throughout this book. 

The residue curve mapping (ROM) technique has traditionally been considered a powerful tool for flowsheet development and preliminary design of conventional multicomponent separation processes. It represents a good approximation of actual equilibrium... 

Certain techniques for the application of thermodynamics in separation technology are introduced in Chapter 11, for example, the concept of residue curve maps, a general procedure for the choice of suitable solvents for the separation of azeotropic systems, the verification of model parameters prior to process simulation and the identification of separation problems. 

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