Use of Negative Compositions

Once the underlying properties and concepts of the negative composition space have been understood, it is now convenient to explore the applications of viewing negative compositions. Example 2.4 shows how nodes placed in negative composition space at 1 atm can in fact be moved. 

Example 2.4 Following on from Example 2.3 using negative compositions, examine the difference in the overall RCM topology when changing system pressure from I to 10 atm for the nonideal acetone/ethanol/methanol system. 

FKjURE 2.19 Entire residue curve map for die nonideal acetone/ethanol/methanol system (with numbered nodes) using die NRTL model at P= 10 atm. 

FIGURE 2.20 CM plot generated in Aspen Plus for the acetone/ethanol/methanol system using the UNIQUAC thermodynamic model AP= 10 atm. 

In the next chapter, an equivalent node-shifting principle will be shown for continuous distillation column sections at the appropriate operating conditions, pinch points can be shifted. Some pinch points move from real space (within the MET) to negative space (outside the MET), and vice versa. Thus, the mode of operation of the piece of equipment can be used to shift unwanted topological features outside the MET. 

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