Residue curve maps limitations

Residue curve maps would be limited usebilness if they could only be generated experimentally. Fortunately that is not the case. The simple distillation process can be described (14) by the set of equations ... 

Even though the simple distillation process has no practical use as a method for separating mixtures, simple distillation residue curve maps have extremely usehil appHcations. These maps can be used to test the consistency of experimental azeotropic data (16,17,19) to predict the order and content of the cuts in batch distillation (20—22) and, in continuous distillation, to determine whether a given mixture is separable by distillation, identify feasible entrainers/solvents, predict the attainable product compositions, quaHtatively predict the composition profile shape, and synthesize the corresponding distillation sequences (16,23—30). By identifying the limited separations achievable by distillation, residue curve maps are also usehil in synthesizing separation sequences combining distillation with other methods. 

Table 8.1 describes the steps of the methodology in more detail. The procedure starts with the Problem definition production rate, chemistry, product specifications, safety, health and environmental constraints, physical properties, available technologies. Then, a first evaluation of feasibility is performed by an equilibrium design. This is based on a thermodynamic analysis that includes simultaneous chemical and physical equilibrium (CPE). The investigation can be done directly by computer simulation, or in a more systematic way by building a residue curve map (RCM), as explained in the Appendix A. This step will identify additional thermodynamic experiments necessary to consolidate the design decisions, mainly phase-equilibrium measurements. Limitations set by chemical equilibrium or by thermodynamic boundaries should be analyzed here. 

The design equations would include, in addition to the usual heat and mass balances and vapor-liquid equilibria, equations for chemical equilibria and/or reaction kinetics. The occurrence of a chemical reaction can severely restrict the allowable ranges of temperatures and phase compositions by virtue of the additional equations for chemical equilibrium/kinetics. This effect can be quantitatively analyzed by constructing a residue curve map (RCM). It explicitly shows the shifting of distillation boundaries in the presence of reaction and defines the limits of feasible distillation column operation. We illustrate this (Venimadhavan et al., 1994) by considering the reaction... 

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